NATIONWIDE MUTUAL INSURANCE CO
SC 14D1/A, 1998-06-10
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<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                 SCHEDULE 14D-1
                              (AMENDMENT NO. 6)
                            TENDER OFFER STATEMENT
      PURSUANT TO SECTION 14(D)(1) OF THE SECURITIES EXCHANGE ACT OF 1934
                                      and
                                SCHEDULE 13D
                  UNDER THE SECURITIES EXCHANGE ACT OF 1934

                               ALLIED GROUP, INC.
                            (NAME OF SUBJECT COMPANY)

                    NATIONWIDE GROUP ACQUISITION CORPORATION
                      NATIONWIDE MUTUAL INSURANCE COMPANY
                                    (Bidders)

                           COMMON STOCK, NO PAR VALUE
                         (Title of Class of Securities)

                                   019220102
                      (CUSIP Number of Class of Securities)

                                W. SIDNEY DRUEN
                   SENIOR VICE PRESIDENT AND GENERAL COUNSEL
                      NATIONWIDE MUTUAL INSURANCE COMPANY
                              ONE NATIONWIDE PLAZA
                              COLUMBUS, OHIO 43215
                           TELEPHONE: (614) 249-7111
            (Name, Address and Telephone Number of Person Authorized
           to Receive Notices and Communications on Behalf of Bidders)

                                 WITH A COPY TO:
                               ERIC M. FOGEL, ESQ.
                             HAROLD W. NATIONS, ESQ.
                                  HOLLEB & COFF
                         55 E. MONROE STREET, SUITE 4100
                             CHICAGO, ILLINOIS 60603
                            TELEPHONE: (312) 807-4600

                            CALCULATION OF FILING FEE

TRANSACTION VALUATION* $1,506,756,211

AMOUNT OF FILING FEE** $301,351

*        For purposes of calculating the filing fee only. This calculation
         assumes the purchase of 31,228,108 shares of common stock, no par
         value (the "Common Shares"), of ALLIED GROUP, INC. (the "Company") at
         $48.25 net per share in cash.

**       The amount of the filing fee, calculated in accordance with Rule
         0-11(d) of the Securities Exchange Act of 1934, as amended, equals
         1/50th of one percent of the aggregate value of cash offered by
         Nationwide Group Acquisition Corporation for such number of Common 
         Shares.
<PAGE>   2


[X]      Check box if any part of the fee is offset as provided by Rule
         0-11(a)(2) and identify the filing with which the offsetting
         fee was previously paid. Identify the previous filing by
         registration statement number, or the Form or Schedule and the
         date of its filing.
         Amount Previously Paid:  $287,960
         Filing Party:  Nationwide Mutual Insurance Company and Nationwide Group
                        Acquisition Corporation
         Form or Registration No.:  Schedule 14D-1
         Date Filed:  May 19, 1998


CUSIP NO. 019220102




1. NAMES OF REPORTING PERSONS
S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON


         Nationwide Mutual Insurance Company (E.I.N.: 31-4177100)


2. CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

   [ ]   (a)

   [ ]   (b)

3. SEC USE ONLY

4. SOURCE OF FUNDS

         WC

5. CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
PURSUANT TO ITEMS 2(e) or 2(f)

6. CITIZENSHIP OR PLACE OF ORGANIZATION

         Ohio

7. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

         1,996,836 Common Shares
         1,827,222 Preferred Shares 

8. CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (7) EXCLUDES CERTAIN
SHARES

9. PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (7)

         6.3% of the Common Shares and 100% of the Preferred Shares 
         representing 21.8% of the voting securities

10.      TYPE OF REPORTING PERSON

         IC






                                       2
<PAGE>   3

CUSIP NO. 019220102

1. NAMES OF REPORTING PERSONS

S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

         Nationwide Group Acquisition Corporation (E.I.N.: 31-1598405)

2. CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
     [ ] (a)
     [ ] (b)

3. SEC USE ONLY

4. SOURCE OF FUNDS

         AF

5. CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED
PURSUANT TO ITEMS 2(e) or 2(f)

6. CITIZENSHIP OR PLACE OF ORGANIZATION

         Ohio

7. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

         1,996,836 Common Shares
         1,827,222 Preferred Shares


8. CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (7) EXCLUDES CERTAIN
SHARES

9. PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (7)

        6.3% of the Common Shares and 100% of the Preferred Shares
        representing 21.8% of the voting securities

10. TYPE OF REPORTING PERSON

         CO

         This Amendment No. 6 amends and supplements the Tender Offer Statement
on Schedule 14D-1 initially filed on May 19, 1998 (as amended, the "Schedule
14D-1") filed with the Securities and Exchange Commission by Nationwide Group
Acquisition Corporation ("Purchaser"), an Ohio corporation and a wholly owned
subsidiary of Nationwide Mutual Insurance Company ("Parent"), an Ohio mutual
insurance company, to purchase all outstanding shares of common stock, no par
value (the "Common Shares"), of Allied Group, Inc., an Iowa corporation, at a
price of $48.25 per Common Share, net to the seller in cash, without interest
thereon, upon the terms and subject to the conditions set forth in the Offer to
Purchase dated May 19, 1998 (the "Offer to Purchase"), as amended and
supplemented by the Supplement thereto, dated June 10, 1998 (the        
"Supplement") and the revised Letter of Transmittal (which, together with any
amendments or supplements thereto, constitutes the "Offer"). Capitalized terms
used and not defined herein shall have the meanings assigned such terms in the
Offer to Purchase, the Supplement or the Schedule 14D-1.
 
ITEM 1.  SECURITY AND SUBJECT COMPANY.

         Item 1 is hereby amended and supplemented by the following:


                                       3
<PAGE>   4
         (b) The information set forth under "Introduction" and Section 1 under
"Terms of the Offer; Expiration Date" in the Supplement annexed hereto as
Exhibit (a)(28) is incorporated herein by reference.

         (c) The information set forth in Section 3 under "Price Range of
Shares; Dividends" in the Supplement is incorporated herein by reference.

ITEM 3.  PAST CONTACTS, TRANSACTIONS OR NEGOTIATIONS WITH THE
         SUBJECT COMPANY.

         Item 3 is hereby amended and supplemented by the following:

         (a)-(b) The information set forth under "Introduction," Section 5,
"Background of the Offer; Contacts with the Company," and Section 6, "Purpose of
the Offer and the Merger; Plans for the Company; Certain Considerations,"  in
the Supplement is incorporated herein by reference.





                                       4
<PAGE>   5

ITEM 4.  SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

         Item 4 is hereby amended and supplemented by the following:
         
         (a) The information set forth in Section 4, "Source and Amount of
Funds" in the Supplement is incorporated herein by reference.

ITEM 5.  PURPOSE OF THE TENDER OFFER AND PLANS OR PROPOSALS OF THE
         BIDDER.

         Item 5 is hereby amended and supplemented by the following:

         The information set forth under "Introduction," Section 5, "Background
of the Offer; Contacts with the Company" and Section 6, "Purpose of the Offer
and the Merger; Plans for the Company; Certain Considerations" in the Supplement
is incorporated herein by reference.


ITEM 6.  INTEREST IN SECURITIES OF THE SUBJECT COMPANY.

         Item 6 is hereby amended and supplemented by the following:
         
         (a) - (b) The information set forth in the Introduction and Schedule I
of the Offer to Purchase and Section 6, "Purpose of the Offer and the Merger;
Plans for the Company; Certain Considerations - The Merger Agreement" in the
Supplement is incorporated herein by reference.

         Pursuant to the irrevocable proxy granted to Purchaser pursuant to the
Shareholder Agreement, dated as of June 3, 1998 between Parent and Allied Mutual
Insurance Company, a copy of which is attached hereto as Exhibit (c)(1), 
Purchaser and Parent may be deemed beneficial owners of 1,827,222
shares of 6-3/4% Series Preferred Stock, no par value (the "Preferred Shares")
and 498,236 shares of Common Stock, no par value (the "Common Shares")
(constituting 17.8% of the outstanding voting securities of the Issuer). None
of the persons identified on Schedule I of the Offer to Purchase (which is
incorporated herein by reference) beneficially owns or has a right to acquire
directly or indirectly any Shares.

         Each of the Parent and the Purchaser has sole voting power with
respect to 1,498,600 of the Common Shares; may be deemed to have shared voting
power with respect to 1,827,222 Preferred Shares and 498,236 Common Shares; has
sole dispositive power with respect to 1,498,600 of the Common Shares; and has  
shared dispositive power with respect to none of the Shares.

         Except as set forth in this Schedule 14D-1, the Parent and the
Purchaser do not know of any other person who has the right to receive or the
power to direct the receipt of dividends from, or the proceeds from the sale of,
the Shares beneficially owned by the Parent or the Purchaser.

ITEM 7.  CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS
         WITH RESPECT TO THE SUBJECT COMPANY'S SECURITIES.

         Item 7 is hereby amended and supplemented by the following:
         
         The information set forth under "Introduction," Section 5, "Background
of the Offer; Contacts with the Company", Section 6, "Purpose of the Offer and
the Merger; Plans for the Company; Certain Considerations" and Section 9,
"Certain Legal Matters; Regulatory Approvals; Certain Litigation" in the
Supplement is incorporated herein by reference.


ITEM 10. ADDITIONAL INFORMATION.

         Item 10 is hereby amended and supplemented by the following:
      
         (f) The information set forth in the Supplement and the revised Letter
of Transmittal, copies of which are attached hereto as Exhibits (a)(28) and
(a)(29), respectively, is incorporated herein by reference.




                                       5
<PAGE>   6
ITEM 11. MATERIAL TO BE FILED AS EXHIBITS.

         (a)     (28)     Supplement to Offer to Purchase, dated June 10, 1998.

                 (29)     Revised Letter of Transmittal.

                 (30)     Revised Notice of Guaranteed Delivery.

                 (31)     Revised Letter to Brokers, Dealers, Commercial Banks,
                          Trust Companies and Other Nominees.

                 (32)     Revised Letter to Clients for use by Brokers, Dealers,
                          Commercial Banks, Trust Companies and Other
                          Nominees.


         (c)     (1)      Shareholder Agreement, dated as of June 3, 1998 
                          between Parent and Allied Mutual Insurance Company.

                                       6
<PAGE>   7

                                   SIGNATURE

         After due inquiry and to the best of its knowledge and belief, the
undersigned certifies that the information set forth in this statement is true,
complete and correct.

Dated:  June 10, 1998

                   NATIONWIDE MUTUAL INSURANCE COMPANY


                   By:      /s/ David A. Diamond
                            -------------------------------
                            Name:   David A. Diamond
                            Title:  Vice President - Enterprise Controller

                   NATIONWIDE GROUP ACQUISITION CORPORATION


                   By:      /s/ Mark B. Koogler
                            -------------------------------
                            Name:   Mark B. Koogler
                            Title:  Vice President - Associate General Counsel






                                       7
<PAGE>   8

                                  EXHIBIT INDEX

(a)(28)            Supplement to Offer to Purchase, dated June 10, 1998.

(a)(29)            Revised Letter of Transmittal.

(a)(30)            Revised Notice of Guaranteed Delivery.

(a)(31)            Revised Letter to Brokers, Dealers, Commercial Banks, Trust
                   Companies and other Nominees.

(a)(32)            Revised Letter to Clients for use by Brokers, Dealers,
                   Commercial Banks, Trust Companies and Other Nominees.


 (c)(1)            Shareholder Agreement, dated as of June 3, 1998
                   between Parent and Allied Mutual Insurance Company.



                                       8

<PAGE>   1
 
             SUPPLEMENT TO THE OFFER TO PURCHASE DATED MAY 19, 1998
 
                    NATIONWIDE GROUP ACQUISITION CORPORATION
                          A WHOLLY OWNED SUBSIDIARY OF
 
                      NATIONWIDE MUTUAL INSURANCE COMPANY
                         HAS INCREASED THE PRICE OF ITS
                               OFFER TO PURCHASE
                     ALL OUTSTANDING SHARES OF COMMON STOCK
                                       OF
 
                               ALLIED GROUP, INC.
                                       TO
 
                          $48.25 NET PER COMMON SHARE
 
           THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M.,
 NEW YORK CITY TIME, ON MONDAY, AUGUST 31, 1998, UNLESS THE OFFER IS EXTENDED.
 
  THE BOARD OF DIRECTORS OF ALLIED GROUP, INC. (THE "COMPANY"), ACTING ON THE
 UNANIMOUS RECOMMENDATION OF A COMMITTEE CONSISTING OF ALL OF THE UNAFFILIATED
DIRECTORS, HAS UNANIMOUSLY DETERMINED THAT THE OFFER AND THE MERGER ARE FAIR TO
    AND IN THE BEST INTERESTS OF THE SHAREHOLDERS OF THE COMPANY (OTHER THAN
NATIONWIDE MUTUAL INSURANCE COMPANY ("PARENT") AND NATIONWIDE GROUP ACQUISITION
 CORPORATION, A WHOLLY OWNED SUBSIDIARY OF PARENT ("PURCHASER")) AND RECOMMENDS
   THAT ALL SHAREHOLDERS OF THE COMPANY ACCEPT THE OFFER, TENDER THEIR SHARES
      PURSUANT TO THE OFFER AND, IF REQUIRED, VOTE IN FAVOR OF THE MERGER.
                            ------------------------
   THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, (1) THERE BEING VALIDLY
 TENDERED AND NOT PROPERLY WITHDRAWN PRIOR TO THE EXPIRATION OF THE OFFER THAT
 NUMBER OF COMMON SHARES WHICH REPRESENT A MAJORITY OF THE COMMON SHARES OF THE
   COMPANY OUTSTANDING ON A FULLY DILUTED BASIS, AND (2) PARENT AND PURCHASER
     HAVING OBTAINED ALL INSURANCE REGULATORY APPROVALS NECESSARY FOR THEIR
 ACQUISITION OF CONTROL OF THE COMPANY AND ITS INSURANCE SUBSIDIARIES ON TERMS
AND CONDITIONS REASONABLY SATISFACTORY TO PURCHASER AND SUCH REGULATORY APPROVAL
   SHALL HAVE BECOME FINAL AND NON-APPEALABLE. SEE SECTION 14 OF THE OFFER TO
  PURCHASE AND SECTION 1 OF THIS SUPPLEMENT. THE OFFER IS NOT CONDITIONED UPON
                         PURCHASER OBTAINING FINANCING.
 
                                   IMPORTANT
 
     Any shareholder desiring to tender all or any portion of such shareholder's
Common Shares should either; (i) complete and sign one of the Letters of
Transmittal (or a facsimile thereof) in accordance with the instructions in the
Letters of Transmittal, have such shareholder's signature thereon guaranteed if
required by Instruction 1 to the Letters of Transmittal, mail or deliver one of
the Letters of Transmittal (or such facsimile thereof) and any other required
documents to the Depositary (as defined herein) and either deliver the
certificates for such Common Shares to the Depositary along with the Letters of
Transmittal (or a facsimile thereof) or deliver such Common Shares pursuant to
the procedures for book-entry transfers set forth in Section 3 of the Offer to
Purchase prior to the expiration of the Offer or (ii) request such shareholder's
broker, dealer, commercial bank, trust company or other nominee to effect the
transaction for such shareholder. A shareholder having Common Shares registered
in the name of a broker, dealer, commercial bank, trust company or other nominee
must contact such broker, dealer, commercial bank, trust company or other
nominee if such shareholder desires to tender such Common Shares.
 
     Any shareholder who desires to tender Common Shares and whose certificates
for such shares are not immediately available, or who cannot comply with the
procedures for book-entry transfers described in the Offer to Purchase as
supplemented by Section 2 of this Supplement on a timely basis, may tender such
Common Shares by following the procedures for guaranteed delivery set forth in
Section 3 of the Offer to Purchase as supplemented by Section 2 of this
Supplement.
 
     Questions and requests for assistance may be directed to the Information
Agent or the Dealer Manager at their respective addresses and telephone numbers
set forth on the back cover of this Supplement. Additional copies of the Offer
to Purchase, this Supplement, the revised Letter of Transmittal or other tender
offer materials may be obtained from the Information Agent.
 
                      The Dealer Manager for the Offer is:
 
                           CREDIT SUISSE FIRST BOSTON
June 10, 1998
<PAGE>   2
 
                               TABLE OF CONTENTS
 
<TABLE>
<S>                                                           <C>
INTRODUCTION................................................     1
1. Terms of the Offer; Expiration Date......................     3
2. Procedures for Tendering Common Shares...................     3
3. Price Range of Shares; Dividends.........................     3
4. Source and Amount of Funds...............................     3
5. Background of the Offer; Contacts with the Company.......     3
6. Purpose of the Offer and the Merger; Plans for the
   Company; Certain Considerations..........................     4
7. Conditions of the Offer..................................    13
8. Certain Legal Matters; Regulatory Approvals; Certain
  Litigation................................................    14
9. Miscellaneous............................................    14
</TABLE>
<PAGE>   3
 
To the Holders of Common Stock
of Allied Group, Inc.:
 
                                  INTRODUCTION
 
     The following information amends and supplements the Offer to Purchase,
dated May 19, 1998 (the "Offer to Purchase"), of Nationwide Group Acquisition
Corporation ("Purchaser"), an Ohio corporation and a wholly owned subsidiary of
Nationwide Mutual Insurance Company, an Ohio mutual insurance company
("Parent"), pursuant to which Purchaser is offering to purchase all outstanding
shares of common stock, no par value (the "Common Shares"), of Allied Group,
Inc., an Iowa corporation (the "Company"), at a price of $48.25 per Common
Share, net to the seller in cash, without interest thereon (the "Offer Price"),
upon the terms and subject to the conditions set forth in the Offer to Purchase,
this Supplement and the revised Letter of Transmittal (which, as amended from
time to time, together constitute the "Offer").
 
     This Supplement should be read in conjunction with the Offer to Purchase.
Except as set forth in this Supplement and the revised Letter of Transmittal,
the terms and conditions previously set forth in the Offer to Purchase, and the
Letter of Transmittal previously mailed to shareholders, remain applicable in
all respects to the Offer. Terms used but not defined herein have the meaning
set forth in the Offer to Purchase or this Supplement.
 
     On June 2, 1998 and June 3, 1998, representatives of Parent and the
Company, together with their legal counsel and financial advisors, held meetings
with respect to the negotiation of a definitive agreement.
 
     On June 3, 1998, the Board of Directors of the Company (the "Company
Board") approved the Agreement and Plan of Merger, dated as of June 3, 1998, by
and among Parent, Purchaser and the Company (the "Merger Agreement").
Thereafter, Parent, Purchaser and the Company entered into the Merger Agreement,
which provides, among other things, for (i) the increase in the Offer Price from
$47.00 per Common Share to $48.25 per Common Share and the modification of the
conditions of the Offer, as described in Section 7 hereof, and (ii) following
the consummation of the Offer, the merger of Purchaser with and into the Company
with the Company continuing as the surviving corporation (the "Merger").
Pursuant to the Merger, each Common Share then outstanding at the effective time
of the Merger (other than Common Shares owned by Parent or Purchaser, shares
held as treasury shares by the Company and Dissenting Shares (as defined in the
Merger Agreement)) will, by virtue of the Merger and without any action by the
holder thereof, be converted into the right to receive $48.25 per Common Share,
net to the shareholder in cash, without interest thereon (the "Merger
Consideration"), upon surrender of the certificate formerly representing such
Common Shares (a "Certificate").
 
     According to the Company's Solicitation/Recommendation Statement on
Schedule 14D-9 (Amendment No. 1) (the "Schedule 14D-9") filed on June 4, 1998
with the Securities and Exchange Commission (the "SEC"), the Company Board,
acting on the unanimous recommendation of a committee consisting of all of the
unaffiliated directors, determined, after consultation with its legal and
financial advisors, and based upon information currently available to it, that
the terms of the Offer as revised to offer cash of $48.25 per Common Share and
the Merger are fair to and in the best interests of the shareholders of the
Company (other than Parent and Purchaser).
 
     The Offer is being amended and supplemented pursuant to the terms of the
Merger Agreement. For a more detailed description of the Merger Agreement, see
Section 6 of this Supplement.
 
     THE BOARD OF DIRECTORS OF THE COMPANY, ACTING ON THE UNANIMOUS
RECOMMENDATION OF A COMMITTEE CONSISTING OF ALL OF THE UNAFFILIATED DIRECTORS,
HAS UNANIMOUSLY DETERMINED THAT THE OFFER AND THE MERGER ARE FAIR TO AND IN THE
BEST INTERESTS OF THE SHAREHOLDERS OF THE COMPANY (OTHER THAN PARENT AND
PURCHASER) AND RECOMMENDS THAT ALL SHAREHOLDERS OF THE COMPANY ACCEPT THE OFFER,
TENDER THEIR SHARES PURSUANT TO THE OFFER AND, IF REQUIRED, VOTE IN FAVOR OF THE
MERGER.
<PAGE>   4
 
     Morgan Stanley & Co., Incorporated ("Morgan Stanley"), financial advisor to
the Company, has delivered its written opinion to the Company Board that the
consideration to be received per Common Share by the holders thereof, in
connection with the Offer and the Merger is fair, from a financial point of
view, to such shareholders. A copy of the opinion of Morgan Stanley is attached
as an exhibit to the Schedule 14D-9. Shareholders are urged to read such opinion
in its entirety for a description of the procedures followed, assumptions and
qualifications made, matters considered and limitations on the review undertaken
by Morgan Stanley.
 
     Because the Company Board approved, on June 3, 1998, the terms of the
Merger Agreement and determined that the Offer and the Merger are fair to and in
the best interest of the Company and its shareholders, the business combination
provisions of Section 490.1110 of the Iowa Business Corporation Act have been
rendered inapplicable to the Merger. Accordingly, the Offer is no longer subject
to the Business Combination Condition.
 
     THE OFFER REMAINS CONDITIONED UPON, AMONG OTHER THINGS, (1) THERE BEING
VALIDLY TENDERED AND NOT PROPERLY WITHDRAWN PRIOR TO THE EXPIRATION OF THE OFFER
THAT NUMBER OF COMMON SHARES WHICH REPRESENT A MAJORITY OF THE COMMON SHARES OF
THE COMPANY OUTSTANDING ON A FULLY DILUTED BASIS, AND (2) PARENT AND PURCHASER
HAVING OBTAINED ALL INSURANCE REGULATORY APPROVALS NECESSARY FOR THEIR
ACQUISITION OF CONTROL OF THE COMPANY AND ITS INSURANCE SUBSIDIARIES ON TERMS
AND CONDITIONS REASONABLY SATISFACTORY TO PURCHASER AND SUCH REGULATORY APPROVAL
SHALL HAVE BECOME FINAL AND NON-APPEALABLE. SEE SECTION 14 OF THE OFFER TO
PURCHASE AND SECTION 1 OF THIS SUPPLEMENT. THE OFFER IS NOT CONDITIONED UPON
PURCHASER OBTAINING FINANCING.
 
     Parent, in addition to entering into the Merger Agreement, has entered into
an Agreement and Plan of Merger, dated as of June 3, 1998 (the "Allied Mutual
Merger Agreement") with Allied Mutual Insurance Company ("Allied Mutual"),
providing for the merger of Allied Mutual with and into Parent (the "Allied
Mutual Merger"). The Allied Mutual Merger Agreement contemplates that,
immediately prior to the consummation of the Allied Mutual Merger, Allied Mutual
would make an extraordinary distribution of $110 million in cash to Allied
Mutual's policyholders. Parent has also entered into an Agreement and Plan of
Merger, dated as of June 3, 1998 (the "Allied Life Merger Agreement") providing
for the merger of a subsidiary of Parent with and into Allied Life Financial
Corporation ("Allied Life"), with Allied Life being the surviving corporation
(the "Allied Life Merger"). In the Allied Life Merger, the holders of the
outstanding shares of common stock of Allied Life (other than Allied Mutual and
holders exercising dissenters' rights of appraisal) would receive $30 per share,
net to the seller in cash, without interest thereon.
 
     The Company has represented to Purchaser and Parent that at the close of
business on June 2, 1998, there were 30,114,827 Common Shares issued and
outstanding, 5,174,437 Common Shares reserved for issuance upon the exercise of
options or other rights to purchase Common Shares under the Company's benefit
plans (of which options or rights with respect to 1,113,281 Common Shares have
been granted) and 1,827,222 shares of 6- 3/4% Series Preferred Stock, no par
value (the "Preferred Shares") issued and outstanding. Each of the Preferred
Shares is entitled to 3.375 votes, which in the aggregate represents
approximately 16.5% of the voting power of the Company on a fully diluted basis
as of June 2, 1998. All of the Preferred Shares are currently held by Allied
Mutual. In connection with the Allied Mutual Merger Agreement, Allied Mutual has
irrevocably granted to Parent's designees, Allied Mutual's proxy to vote any
securities (including the Preferred Shares) owned by Allied Mutual at any
shareholders meeting (i) in favor of the Merger, and (ii) against any
alternative transaction or frustrating transaction. See "Purpose of the Offer
and the Merger; Plans for the Company; Certain Considerations -- Shareholder
Agreement."
 
     Based on the foregoing, there would be 31,228,108 Common Shares outstanding
on a fully diluted basis. The Purchaser believes that approximately 15,614,055
Common Shares represent a majority of the Common Shares of the Company.
Accordingly, Purchaser believes that the Minimum Condition would be satisfied if
an aggregate of 15,614,055 Common Shares are validly tendered pursuant to the
Offer.
 
                                        2
<PAGE>   5
 
     THE OFFER TO PURCHASE, THIS SUPPLEMENT AND THE REVISED LETTER OF
TRANSMITTAL CONTAIN IMPORTANT INFORMATION WHICH SHOULD BE READ CAREFULLY BEFORE
ANY DECISION IS MADE WITH RESPECT TO THE OFFER.
 
1. TERMS OF THE OFFER; EXPIRATION DATE.
 
     The discussion set forth in Section 1 of the Offer to Purchase is hereby
amended and supplemented as follows:
 
     The term "Expiration Date" has been amended to mean 5:00 P.M., New York
City time, on Monday, August 31, 1998, unless and until Purchaser, in its sole
discretion, but subject to the terms of the Merger Agreement, shall have
extended the period of time during which the Offer is open, in which event the
term "Expiration Date" shall refer to the latest time and date at which the
Offer, as so extended by Purchaser, shall expire. So long as the Merger
Agreement is in effect, and the Offer Conditions (as defined below) have not
been satisfied or waived, Purchaser shall not, and Parent shall not cause
Purchaser to, have the Offer expire. See Section 6, "Purpose of the Offer and
the Merger; Plans for the Company; Certain Considerations-The Merger
Agreement-The Offer."
 
     It is Parent's and Purchaser's current expectation that the Form A hearing
in Iowa will be held at the end of July 1998. A hearing date has not established
with the Arizona Insurance Commissioner. Since the Offer remains conditional
upon the satisfaction of the Insurance Regulatory Condition, the Purchaser is
currently extending the Expiration Date to August 31, 1998 to provide sufficient
time for the Form A hearing in Iowa and any order to become final and
non-appealable. Depending on the outcome of the Iowa Form A hearing and the
hearing to be held in Arizona, it is possible that the Offer may be extended one
or more times, which time periods may, in the aggregate, be significant.
 
2. ACCEPTANCE FOR PAYMENT AND PAYMENT FOR COMMON SHARES.
 
     The discussion set forth in Section 3 of the Offer to Purchase is hereby
amended and supplemented as follows:
 
     The revised Letter of Transmittal and the revised Notice of Guaranteed
Delivery distributed with this Supplement may be used to tender Common Shares.
Tendering shareholders may also continue to use the Letter of Transmittal and
Notice of Guaranteed Delivery previously distributed with the Offer to Purchase
to tender Common Shares.
 
     SHAREHOLDERS WHO HAVE PREVIOUSLY VALIDLY TENDERED COMMON SHARES PURSUANT TO
THE OFFER AND NOT PROPERLY WITHDRAWN SUCH COMMON SHARES HAVE VALIDLY TENDERED
SUCH COMMON SHARES FOR PURPOSES OF THE OFFER, AS AMENDED, AND NEED NOT TAKE ANY
FURTHER ACTION IN ORDER TO RECEIVE THE PRICE OF $48.25 PER COMMON SHARE PURSUANT
TO THE OFFER.
 
3. PRICE RANGE OF SHARES; DIVIDENDS.
 
     The discussion set forth in Section 6 of the Offer to Purchase is hereby
amended and supplemented as follows:
 
     According to public sources, the high and low closing sale prices per
Common Share on the NYSE for the Second Quarter of 1998 (through June 9, 1998)
were $46 9/16 and $26.00 respectively. On June 3, 1998, the last full trading
day prior to the announcement of the Merger Agreement, the last reported closing
price on the NYSE Composite Tape was $46 3/16 per Common Share. SHAREHOLDERS ARE
URGED TO OBTAIN A CURRENT MARKET QUOTATION FOR THE COMMON SHARES.
 
                                        3
<PAGE>   6
 
4. SOURCE AND AMOUNT OF FUNDS.
 
     The discussion set forth in Section 10 of the Offer to Purchase is hereby
amended and supplemented as follows:
 
     Purchaser estimates that the total amount of funds now required to purchase
Common Shares pursuant to the Offer (as described in this Supplement) and to pay
all related costs and expenses, will be approximately $1.55 billion. Purchaser
plans to obtain all funds needed for the Offer through a capital contribution
from Parent. Parent plans to obtain such funds entirely from existing cash
accounts. Parent has in excess of $7.0 billion available for such purpose.
 
5. BACKGROUND OF THE OFFER; CONTACTS WITH THE COMPANY.
 
     The discussion set forth in Section 11 of the Offer to Purchase is hereby
amended and supplemented as follows:
 
     On May 28, 1998, Parent, Purchaser and the Company entered into an
agreement as to the confidentiality of settlement discussions on or before June
2, 1998 regarding the litigation filed by Parent. Beginning on May 28, 1998,
representatives of Parent's financial advisor met with representatives of the
Company's financial advisor on several occasions to discuss the terms of the
Offer and whether a negotiated transaction could be achieved. On May 29, 1998,
Parent delivered to the Company a draft merger agreement.
 
     On June 1, Parent indicated that it was prepared to increase its Offer to
$48.25 per Common Share as part of a negotiated merger agreement and to reduce
the amount of the termination fee that would be payable under certain
circumstances pursuant to Parent's and Purchaser's proposed merger agreement. On
June 1, the Company's financial advisor informed Parent that the Company Board
determined that it was prepared in principle to recommend a transaction at that
price and with the revised termination fee provision, subject to negotiation of
an acceptable definitive agreement.
 
     On June 2, 1998 and June 3, 1998, representatives of Parent and the
Company, together with their legal counsel and financial advisors, held meetings
with respect to the negotiation of a definitive agreement.
 
     On June 3, 1998, the Company Board approved the Merger Agreement.
Thereafter, Parent, Purchaser and the Company entered into the Merger Agreement,
which provides, among other things, for (i) the increase in the Offer Price from
$47.00 per Common Share to $48.25 per Common Share and the modification of the
conditions of the Offer, as described in Section 7 hereof, and (ii) following
the consummation of the Offer, the Merger. Pursuant to the Merger, each Common
Share then outstanding at the effective time of the Merger (other than Common
Shares owned by Parent or Purchaser, shares held as treasury shares by the
Company and Dissenting Shares (as defined in the Merger Agreement)) will, by
virtue of the Merger and without any action by the holder thereof, be converted
into the right to receive $48.25 per Common Share, net to the shareholder in
cash, without interest thereon, upon surrender of the Certificate.
 
6. PURPOSE OF THE OFFER AND THE MERGER; PLANS FOR THE COMPANY; CERTAIN
   CONSIDERATIONS.
 
     The discussion set forth in Section 12 of the Offer to Purchase is hereby
amended and supplemented as follows:
 
The Merger Agreement
 
     Pursuant to the Merger Agreement and following the consummation of the
Offer, Parent, Purchaser and the Company have agreed to effect the Merger in
accordance with the provisions of the Merger Agreement as promptly as
practicable following the satisfaction or waiver of certain conditions to the
Merger. Set forth below is a description of the material provisions of the
Merger Agreement.
 
     The Offer.  In the Merger Agreement, the Purchaser has agreed, subject to
certain conditions, and among other things, to amend the Offer (a) to increase
the purchase price offered from $47 per Common Share to $48.25 per Common Share,
net to the seller in cash without interest, and (b) to modify the conditions of
the Offer to those set forth below under Section 7. The Merger Agreement
provides that, without
                                        4
<PAGE>   7
 
the consent of the Company, the Purchaser shall not (a) reduce the number of
Common Shares sought in the Offer, (b) reduce the Offer price to a price less
than $48.25 per Common Share, (c) change or add to the conditions set forth
below under Section 7, (d) except as provided in the next sentence, extend the
Offer, (e) change the form of consideration payable in the Offer (f) waive the
Minimum Condition or the Insurance Regulatory Condition without the Company's
consent, or (g) amend any other term of the Offer in any manner adverse to the
holders of the Shares.
 
     Notwithstanding the foregoing, Purchaser may, without the consent of the
Company, (A) extend the Offer, if at the scheduled or extended expiration date
of the Offer any of the conditions to the Purchaser's obligation to purchase the
Common Shares shall not be satisfied or waived, until such time as such
conditions are satisfied or waived, (B) extend the Offer for any period required
by any rule, regulation, interpretation or position of the SEC or the staff
thereof applicable to the Offer and (C) extend the Offer for any reason on one
or more occasions for an aggregate period of not more than 10 business days (for
all such extensions) pursuant to this clause (C) beyond the latest expiration
date that would otherwise be permitted under clause (A) or (B) of this sentence.
So long as the Merger Agreement is in effect, and the Offer Conditions (as
defined below) have not been satisfied or waived, Purchaser shall not, and
Parent shall not cause Purchaser to, have the Offer expire. Subject to the terms
and conditions of the Offer and the Merger Agreement, Purchaser shall, and
Parent shall cause Purchaser to, accept for payment, and pay for, all Common
Shares validly tendered and not withdrawn pursuant to the Offer that Purchaser
becomes obligated to accept for payment, and pay for, pursuant to the Offer, as
soon as practicable after the expiration of the Offer.
 
     The Merger.  The Merger Agreement provides that, following the satisfaction
or waiver of the conditions set forth therein, Purchaser will be merged with and
into the Company, with the Company continuing as the surviving corporation (the
"Surviving Corporation"), and each Common Share then outstanding (other than
Common Shares owned by Parent or Purchaser, shares held as treasury shares by
the Company and Dissenting Shares) will, by virtue of the Merger and without any
action by the holder thereof, be converted into the right to receive $48.25 per
Common Share, net to the shareholder in cash, without interest thereon, upon the
surrender of the Certificate formerly representing such Shares.
 
     Representations and Warranties.  The Merger Agreement contains
representations and warranties by the Company with respect to, among other
things, the organization, qualification and capitalization of the Company, the
subsidiaries of the Company, the authority of the Company relative to the Merger
Agreement, the absence of violations of law, required governmental filings, the
statutory financial statements of the Company's insurance company subsidiaries
and their actuarial reserves, the SEC filings of the Company, the absence of
certain changes or events and of any undisclosed liabilities, the
inapplicability of state takeover statutes, compliance with applicable laws, the
assets of the Company, environmental matters, contracts of the Company, taxes
and tax returns, benefit plans, labor relations, intellectual property,
transactions with affiliates, voting requirements applicable to the Merger and
the status of the Company's subsidiaries as regulated investment companies.
 
     The Merger Agreement also contains representations and warranties of Parent
and Purchaser with respect to, among other things, their organization and
qualification, their authority relative to the Merger Agreement, the absence of
violations of law, required governmental filings, the absence of certain
litigation, and their financial ability to perform.
 
     Covenants of the Company.  In the Merger Agreement, the Company has
covenanted and agreed that, among other things, during the period from the date
of the Merger Agreement until the effective time of the Merger (the "Effective
Time"), unless Parent shall otherwise agree in writing, or except as otherwise
contemplated in the Merger Agreement, the Company and its subsidiaries shall
conduct their respective businesses in the ordinary course consistent with past
practice and shall use all reasonable efforts to preserve intact their business
organizations and relationships with third parties (including but not limited to
their respective relationships with policyholders, insureds, agents,
underwriters, brokers and investment customers), and to keep available the
services of their present officers and key employees, subject to the terms of
the Merger Agreement. In addition, except as otherwise contemplated by the
Merger Agreement, from the date thereof until the Effective Time, without the
prior written consent of Parent, (a) the Company shall not adopt
 
                                        5
<PAGE>   8
 
or propose any change in its Restated Articles of Incorporation or Bylaws; (b)
the Company shall not declare, set aside or pay any dividend or other
distribution with respect to any shares of capital stock of the Company, except
for regular quarterly dividends payable in an amount no greater than $0.14 per
share on the Common Shares and the regular quarterly dividends per share on the
Preferred Shares, or split, combine or reclassify any of the Company's capital
stock, and the Company and its subsidiaries shall not repurchase, redeem or
otherwise acquire any shares of capital stock or other securities of, or other
ownership interests in, the Company; (c) the Company shall not, and shall not
permit any of its subsidiaries to, merge or consolidate with any other person or
(except in the ordinary course of business) acquire a material amount of assets
of any other person; (d) the Company shall not, and shall not permit any
subsidiary to, sell, lease, license or otherwise surrender, relinquish or
dispose of (i) any material facility owned or leased by the Company or any of
its subsidiaries or (ii) any assets or property which are material to the
Company and its subsidiaries taken as a whole, except pursuant to existing
contracts or commitments, or in the ordinary course of business consistent with
past practice; (e) the Company shall not, and shall not permit any of its
subsidiaries to, settle any material audit, make or change any material tax
election or file materially amended tax returns; (f) the Company and its
subsidiaries shall not issue any capital stock or other securities or enter into
any amendment of any material term of any outstanding security of the Company,
and the Company and its subsidiaries shall not incur any material indebtedness
except in the ordinary course of business pursuant to existing credit facilities
or arrangements, amend or otherwise increase, accelerate the payment or vesting
of the amounts payable or to become payable under or fail to make any required
contribution to, any Benefit Plan (as defined in the Merger Agreement) or
materially increase any non-salary benefits payable to any employee or former
employee, except in the ordinary course of business consistent with past
practice or as otherwise permitted by the Merger Agreement; (g) the Company
shall not, and shall not permit any of its subsidiaries to, grant any increase
in the compensation or benefits of directors, officers, employees, consultants
or agents of the Company or any of its subsidiaries other than increases in the
ordinary course of business consistent with past practice; (h) the Company shall
not, and shall not permit any of its subsidiaries to, enter into or amend any
employment agreement or other employment arrangement with any employee of the
Company or any of its subsidiaries, except in the ordinary course of business
consistent with past practices (which past practices shall not be deemed to
include actions taken in connection with the Merger); (i) the Company shall not
change any method of accounting or accounting practice by the Company or any of
its subsidiaries, except for any such required change in GAAP or SAP (as such
terms are defined in the Merger Agreement); (j) the Company shall not permit any
Allied Insurer (as such term is defined in the Merger Agreement) to conduct
transactions in investment assets except in compliance with the investment
policies of such Allied insurance subsidiaries in effect on the date hereof and
all applicable insurance laws and regulations; (k) the Company shall not, and
shall not permit any of its subsidiaries to, enter into any agreement to
purchase, or to lease for a term in excess of one year, any real property,
provided that the Company, or any of its subsidiaries, (i) may as a tenant, or a
landlord, renew any existing lease for a term not to exceed eighteen months and
(ii) may, in its capacity as a landlord, renew any lease pursuant to an option
granted prior to the date hereof; and (l) none of the Allied insurance
subsidiaries may make any material change in its underwriting, claims management
or reserving practices.
 
     In addition to the foregoing, the Company has agreed that, except to the
extent necessary to comply with the requirements of applicable laws and
regulations, it shall not, and shall not permit any of its subsidiaries to, (a)
take, or agree or commit to take, any action that would make any representation
and warranty of the Company in the Merger Agreement inaccurate in any material
respect at, or as of any time prior to, the Effective Time, (b) omit, or agree
or commit to omit, to take any action necessary to prevent any such
representation or warranty from being inaccurate in any material respect at any
such time, provided however, that the Company shall be permitted to take or omit
to take such action which (without any uncertainty) can be cured, and in fact is
cured, at or prior to the Effective Time or (c) take, or agree to commit to
take, any action that would result in, or is reasonably likely to result in, any
of the conditions of the Merger set forth in the Merger Agreement not being
satisfied.
 
     Prohibition on Solicitation.  Pursuant to the Merger Agreement, the Company
has agreed that it will not, and will not permit or cause any of its
subsidiaries or any of the officers or directors of it or its subsidiaries to,
and shall direct its and its subsidiaries' employees, agents and representatives
(including any investment
                                        6
<PAGE>   9
 
banker, attorney or accountant retained by it or any of its subsidiaries) not
to, directly or indirectly, initiate, solicit, encourage or otherwise facilitate
any inquiries or the making of any proposal or offer with respect to a merger,
reorganization, share exchange, consolidation or similar transaction involving,
or any purchase of 20 percent or more of the assets or any equity securities of,
the Company or any of its Significant Subsidiaries (as defined in Regulation S-X
promulgated by the SEC) other than as set forth in the Allied Disclosure Letter,
or another business combination (any such proposal or offer, an "Acquisition
Proposal").
 
     The Merger Agreement further provides that the Company will not, and will
not permit or cause any of its subsidiaries or any of the officers and directors
of it or its subsidiaries to, and shall direct its, and its subsidiaries'
employees, agents and representatives (including any investment banker, attorney
or accountant retained by it or any of its subsidiaries) to, directly or
indirectly, engage in any negotiations concerning, or provide any confidential
information or data to, or have any discussions with, any person relating to an
Acquisition Proposal, whether made before or after the date of the Merger
Agreement, or otherwise facilitate any effort or attempt to make or implement an
Acquisition Proposal; provided, however, that nothing contained in the Merger
Agreement shall prevent the Company or the Company Board from (i) complying with
Rule 14e-2 promulgated under the Exchange Act with regard to an Acquisition
Proposal or (ii) at any time prior to the payment for Common Shares pursuant to
the Offer (A) providing information in response to a request therefor by a
person who has made an unsolicited bona fide written Acquisition Proposal if the
Company Board receives from such person an executed confidentiality agreement on
customary terms; (B) engaging in any negotiations or discussions with any person
who has made an unsolicited bona fide written Acquisition Proposal; or (C)
recommending such an Acquisition Proposal to the shareholders of the Company, if
and only to the extent that, (i) in each such case referred to in clause (A),
(B) or (C) above, the Company Board determines in good faith after consultation
with outside legal counsel that such action is reasonably likely to be necessary
in order for its directors to comply with their respective fiduciary duties
under applicable law and (ii) in the case referred to in clause (C) above, the
Company Board determines in good faith (after consultation with its financial
advisor) that such Acquisition Proposal, if accepted, is reasonably likely to be
consummated, taking into account all legal, financial and regulatory aspects of
the proposal and the person making the proposal and would, if consummated,
result in a more favorable transaction than the transaction contemplated by the
Merger Agreement, taking into account the long-term prospects and interests of
the Company and its shareholders.
 
     The Company has agreed in the Merger Agreement to immediately cease and
cause to be terminated any existing activities, discussions or negotiations with
any parties conducted heretofore with respect to any of the foregoing, and to
notify Parent immediately if any such inquiries, proposals or offers are
received by, any such information is requested from, or any such discussions or
negotiations are sought to be initiated or continued with, any of its
representatives indicating, in connection with such notice, the name of such
person and the material terms and conditions of any proposals or offers and
thereafter shall keep Parent informed, on a reasonably current basis, of the
status and terms of any such proposals or offers and the status of any such
negotiations or discussions.
 
     If, prior to the purchase of Common Shares pursuant to the Offer, there is
an Acquisition Proposal which the Company Board determines represents a more
favorable transaction to the Company and its shareholders than the transactions
contemplated by the Merger Agreement, and if the Company Board, after
consultation with outside counsel, shall have determined that failure to
terminate the Merger Agreement is reasonably likely to be inconsistent with the
fiduciary duties of the Company Board under applicable law, the Company may
terminate the Merger Agreement. If the Company so elects to terminate the Merger
Agreement, the Company shall, immediately prior to any such termination, pay a
termination fee in the amount of $30 million in immediately available funds by
wire transfer to a bank account designated by Parent.
 
     Stockholder Approval; Preparation of Proxy Statement.  The Merger Agreement
provides that as soon as practicable following the purchase of the Common Shares
pursuant to the Offer, the Company shall prepare and file with the SEC the Proxy
Statement, if required by applicable law. The Company will use its reasonable
best efforts to cause the Proxy Statement to be mailed to its shareholders as
promptly as practicable. Parent and Purchaser will use their reasonable best
efforts to assist the Company in the preparation and filing of the Proxy
Statement.
                                        7
<PAGE>   10
 
     Subject to the fiduciary obligations of the Company Board, as described
above, the Merger Agreement provides that following the purchase of Shares in
the Offer, if Parent and its subsidiaries shall not following such purchase own
at least 90% of the Company's outstanding Common Shares and 90% of the Company's
outstanding Preferred Shares, the Company will take all actions necessary in
accordance with applicable law and its Articles of Incorporation and By-laws to
convene a meeting, if required by applicable law, of its shareholders (the
"Shareholders Meeting") to consider and vote upon the approval of the Merger
Agreement and the Merger. Subject to the fiduciary obligations of the Company
Board, as described above, the Merger Agreement further provides that the
Company will, through the Company Board, recommend to its shareholders approval
of the Merger Agreement and the Merger, and that the Company will use its
reasonable best efforts to hold the Shareholders Meeting (unless, following the
purchase of Common Shares in the Offer, Parent and its subsidiaries own at least
90% of the Company's outstanding Common Shares and 90% of the Company's
outstanding Preferred Shares), as soon as practicable after the date of the
Merger Agreement.
 
     For a description of the short-form merger provisions of the Iowa Business
Corporation Law, which, under certain circumstances, could be applicable to the
Merger, see the introduction to the Purchaser's Offer to Purchase.
 
     Access to Information.  Pursuant to the Merger Agreement, subject to
applicable law, the Company (a) shall afford to Parent's and Purchaser's
accountants, legal counsel and other advisors ("Representatives") full access
during normal business hours through the period immediately prior to the
Effective Time to all of its and its Significant Subsidiaries' assets, books,
contracts, commitments and records (including, but not limited to, tax returns),
and (b) during such period, shall furnish promptly to Parent and Purchaser all
such information concerning its business, assets and personnel or those of any
of its affiliates, in either clause (a) or (b), as Parent or Purchaser may
reasonably request. Unless otherwise required by law, Parent and Purchaser will,
and will cause their Representatives to, hold any such information in confidence
until such time as such information otherwise becomes publicly available through
no wrongful act of Parent, Purchaser or their Representatives. In the event of
the termination of the Merger Agreement for any reason, Parent will, and will
cause Purchaser and their respective Representatives to, return to the Company
all copies of written information furnished by the Company or its
Representatives to Parent, Purchaser and their Representatives and destroy all
memoranda, notes and other writings prepared by Parent, Purchaser or their
Representatives based upon or including the information furnished by the Company
or any of its Representatives to Parent, Purchaser or their Representatives (and
Parent will certify to the Company that such destruction has occurred) and
neither Parent nor Purchaser shall use any such information for any purpose.
Prior to the completion of the Offer and, if the Merger Agreement is terminated,
during the two-year period following the date of termination, Parent will not
(and will not assist or encourage others, including its subsidiaries, to)
solicit the services, as employee, consultant or otherwise, of any employee of
the Company, provided, that nothing in the Merger Agreement shall be deemed to
prohibit general solicitations of employment of persons in Parent's ordinary
course of business not directed specifically toward employees of the Company,
solicitations through executive recruiting firms not directed specifically
toward employees of the Company or employees that make contact with Parent.
 
     Reasonable Best Efforts.  Each of the parties to the Merger Agreement
agrees to use its reasonable best efforts to take, or cause to be taken all
action, to do, or cause to be done, and to assist and cooperate with the other
parties in doing or causing to be done, all things necessary, proper or
advisable to consummate and make effective, in the most expeditious manner
practicable, the transactions contemplated by the Merger Agreement, including,
but not limited to, (i) the holding of the Shareholders Meeting and the
preparation of the Proxy Statement, (ii) the obtaining of all governmental
approvals, and all other necessary actions or nonactions, waivers, consents and
approvals from all appropriate governmental entities and other persons and the
making of all necessary registrations and filings, (iii) the obtaining of the
opinions and other documents that are conditions to the closing of the Merger,
(iv) the resolution of all organizational and human resources issues relating to
the transactions contemplated by the Merger Agreement, (v) the obtaining or
making of all consents, environmental permits, filings or licenses necessary or
desirable to ensure that the business of the Surviving Corporation may be
conducted without disruption consistent with the past practice of each of the
constituent companies to the Merger and (vi) the defending of any legal
proceedings challenging the Merger
 
                                        8
<PAGE>   11
 
Agreement or the consummation of the transactions contemplated thereby, the
defense of which shall, at the request of either the Company or Parent, be
conducted jointly by Parent and the Company on a basis that is satisfactory to
both the Company and Parent. The Company grants Parent the right to decide for
purposes of the insurance regulatory hearings whether to submit regulatory
applications for the Company, Allied Life and Allied Mutual concurrently or
separately, and whether to conduct the regulatory hearing and approval
proceedings concurrently or separately for each of the Company, Allied Life and
Allied Mutual. Both the Company and Parent agree to use their reasonable best
efforts to coordinate and cooperate during the regulatory approval process.
 
     Certain Litigation.  In connection with the execution of the Merger
Agreement, Parent and Purchaser agreed from and after the date of the Merger
Agreement and until the Effective Time, to cease, in any and all respects, the
prosecution of any litigation against the Company or any of its affiliates. In
addition, Parent and Purchaser agreed that immediately following the Effective
Time, they would dismiss, with prejudice, any and all litigation brought by them
against the Company or against its affiliates. See Section 8 of this Supplement.
 
     Board of Directors; Corporate Governance.  Promptly upon acceptance for
payment of the Common Shares by Purchaser pursuant to the Offer, Purchaser shall
be entitled to designate such number of directors on the Company Board as will
give Purchaser, subject to compliance with Section 14(f) of the Exchange Act, a
majority of such directors, and the Company shall, at such time, cause
Purchaser's designees to be so elected by its existing Company Board and each
subsidiary of the Company and each committee of the Company Board and each such
Subsidiary as will give Purchaser a majority of such directors or committee, and
the Company shall, at such time, cause Purchaser's designees to be so elected.
Subject to applicable law, the Company shall take all action requested by Parent
necessary to effect any such election. In connection with the foregoing, the
Company will promptly, at the option of Parent, either increase the size of the
Company Board and/or obtain the resignation of such number of its current
directors as is necessary to enable Purchaser's designees to be elected or
appointed to the Company Board.
 
     Treatment of Stock Options; Certain Benefits.  Pursuant to the Merger
Agreement, as of immediately prior to the Effective Time each option to acquire
Common Shares (each, an "Option"), restricted stock award ("Restricted Stock")
or stock appreciation right ("SARs" and, together with the Options and
Restricted Stock, the "Awards") outstanding under any of the Company's Long-Term
Management Incentive Plan, the Nonqualified Stock Option Plan, the Stock Option
Plan, the Executive Equity Incentive Plan or any other similar plan, arrangement
or agreement (together, the "Company Plans"), whether or not then exercisable or
vested, shall become fully exercisable and vested and shall be canceled or
repurchased and, in consideration of such cancellation or repurchase, the
Company shall pay to the holder of such Award an amount in respect thereof equal
to the product of (A) the Applicable Amount, multiplied by (B) the number of
shares subject thereto (such payment to be net of applicable withholding taxes).
The term "Applicable Amount" shall mean (i) in the case of Awards of Restricted
Stock, the Merger Consideration, (ii) in the case of Awards of Options, the
excess of (A) the Merger Consideration over (B) the exercise price of such
Option or (iii) in the case of Awards of SARs, the excess of (A) the Merger
Consideration over (B) the grant price of such SAR.
 
     The Merger Agreement provides that, for a period of at least one year
following the Effective Time, Parent shall provide each employee or former
employee of the Company or any of its subsidiaries with (i) the same basic
compensation (including base salary, wages or commissions) and annual incentive
opportunity, to the extent applicable, and (ii) benefits, which, not
individually but in the aggregate, are substantially comparable, in each case to
the compensation and benefits that were provided to such employee or former
employee by the Company or any of its subsidiaries (including, but not limited
to, any Allied Benefit Plan) as of immediately prior to the Effective Time,
provided that the foregoing items (i) and (ii) shall not be deemed to require
Parent to offer an employee stock ownership plan or other equity related
arrangement. Parent is not required to continue any such employee's employment
following the Effective Time, provided, however, that, in the event that any
such employee is terminated involuntarily following the Effective Time and prior
to the first anniversary thereof by action of Parent or any of its subsidiaries,
such employee shall receive at least the same severance and termination benefits
as he or she would have received under the terms of the applicable Allied
Benefit Plan, as in effect immediately prior to the Effective Time. From and
after the Effective Time,
                                        9
<PAGE>   12
 
for purposes of determining eligibility, but not for purposes of benefit accrual
under the Parent defined benefit plan, and for purposes of determining
entitlement to vesting and entitlement to vacation, severance and other benefits
for employees under any compensation, severance, welfare, pension (but not for
purposes of benefit accrual), benefit, savings or other plan of Parent or any of
its subsidiaries in which employees of the Company or any of its subsidiaries
become eligible to participate, service with the Company or any of its
subsidiaries shall be credited as if such service had been rendered to Parent or
such Purchaser subsidiary; provided that Parent may, in lieu of providing
retiree medical coverage under Parent's retiree medical plan, cause the Company
to continue to offer its retiree medical plan as currently in effect to its
current and former employees. For purposes of each outstanding Company
short-term, mid-term and long-term incentive award held by any Company employee
that is based in whole or in part on the achievement of any performance or other
similar criteria, such award shall be adjusted, as determined by Parent in
consultation with the Company, to reflect factors that adversely impact the
opportunity of such Allied employee to achieve such performance or other
criteria, and which shall include financial advisory, legal and other expenses
incurred in connection with the transactions contemplated by this Agreement.
 
     Indemnification and Insurance.  The Merger Agreement provides that, in the
event of any threatened or actual claim, action, suit, proceeding or
investigation, whether civil, criminal or administrative, including, without
limitation, any such claim, action, suit, proceeding or investigation by or in
the right of the Company or any of its subsidiaries, in which any of the present
officers or directors (the "Indemnified Parties") of the Company or any of its
subsidiaries is, or is threatened to be, made a party by reason of the fact that
he or she is or was a director, officer, employee or agent of the Company or any
of its subsidiaries, or is or was serving at the request of the Company or any
of its subsidiaries as a director, officer, employee or agent of another
corporation, partnership, joint venture, trust or other enterprise, whether
before or after the Effective Time, the parties to the Merger Agreement will
cooperate and use their best efforts to defend against and respond thereto. It
is understood and agreed that the Company shall indemnify and hold harmless, and
after the Effective Time the Surviving Corporation and Parent, jointly and
severally, shall indemnify and hold harmless, as and to the full extent
permitted by applicable Law, each such Indemnified Party against any losses,
claims, damages, liabilities, costs, expenses (including reasonable attorneys'
fees and expenses), judgments, fines and amounts paid in settlement in
connection with any such claim, action, suit, proceeding or investigation, and,
in the event of any such claim, action, suit, proceeding or investigation
(whether arising before or after the Effective Time), (i) the Indemnified
Parties may retain one counsel satisfactory to them unless there are conflicts
under applicable professional standards, and the Company, or the Surviving
Corporation and Parent after the Effective Time, shall pay all reasonable fees
and expenses of such counsel for the Indemnified Parties promptly as statements
therefor are received and (ii) the Company and the Surviving Corporation and
Parent will use their respective reasonable best efforts to assist in the
vigorous defense of any such matter; provided, that neither the Company nor the
Surviving Corporation nor Parent shall be liable for any settlement effected
without its prior written consent (which consent shall not be unreasonably
withheld); and provided further that the Surviving Corporation and Parent shall
have no obligation under the Merger Agreement to any Indemnified Party when and
if a court of competent jurisdiction shall ultimately determine, and such
determination shall have become final and non-appealable, that indemnification
of such Indemnified Party in the manner contemplated by the Merger Agreement is
prohibited by applicable law.
 
     The Merger Agreement further provides that Parent shall cause the Surviving
Corporation to keep in effect in its By-Laws a provision for a period of not
less than six years from the Effective Time (or, in the case of matters
occurring prior to the Effective Time which have not been resolved prior to the
sixth anniversary of the Effective Time, until such matters are finally
resolved) which provides for indemnification of the Indemnified Parties to the
full extent permitted by applicable law.
 
     In addition, the Merger Agreement provides that Parent shall cause to be
maintained in effect, for not less than six years from the Effective Time, the
current policies of the directors' and officers' liability insurance maintained
by the Company (provided that Parent may substitute therefor policies of at
least the same coverage containing terms and conditions which are no less
advantageous) with respect to matters occurring prior to the Effective Time;
provided, however, that if the aggregate annual premiums for such insurance at
any time during such period shall exceed 200% of the per annum rate of premium
currently paid by the
 
                                       10
<PAGE>   13
 
Company and its Subsidiaries for such insurance on the date of the Merger
Agreement, then Parent shall cause the Company (or the Surviving Corporation if
after the Effective Time) to, and the Company (or the Surviving Corporation if
after the Effective Time) shall, provide the maximum coverage that shall then be
available at an annual premium equal to 200% of such rate, and Parent, in
addition to the indemnification described above, shall indemnify the Indemnified
Parties for the balance of such insurance coverage on the same terms and
conditions as though Parent were the insurer under those policies.
 
     Conditions to the Merger.  The respective obligation of each party to the
Merger Agreement to effect the Merger shall be subject to the satisfaction,
prior to the closing of the transactions contemplated by the Merger Agreement,
of the following conditions: (a) the Offer shall have been successfully
completed; (b) if required by applicable law, the Merger Agreement and the
Merger shall have been approved and adopted by the vote of the shareholders of
the Company at the Shareholders Meeting called for such purpose; and (c) no
order entered or law promulgated or enacted by any governmental entity shall be
in effect which would prevent the consummation of the Merger or any other
material transactions completed by the Merger Agreement, and no proceeding
brought by a governmental entity shall have been commenced and be pending which
seeks to restrain, enjoin, prevent, or materially delay or restructure the
Merger or any other material transactions contemplated by the Merger Agreement.
 
     Termination.  The Merger Agreement may be terminated and the Merger
abandoned at any time prior to the Effective Time, whether before or after
approval of the Merger by the shareholders of Parent or of Allied: (a) by mutual
consent of Parent and the Company; (b) by Parent, if the Board of Directors of
the Company withdraws its recommendation to the Company's shareholders to
approve the Merger; (c) by Parent or the Company, if consummation of the Merger
is barred by a permanent injunction which is final and non-appealable; (d) by
the Company, if prior to the purchase of Common Shares pursuant to the Offer,
there is an Acquisition Proposal which the Company Board determines represents a
more favorable transaction to the Company and its shareholders than the
transactions contemplated by the Merger Agreement, and if the Company Board,
after consultation with outside counsel, shall have determined that failure to
terminate the Merger Agreement is reasonably likely to be inconsistent with the
fiduciary duties of the Company Board under applicable law; (e) by the Company
prior to the completion of the Offer, upon a material breach of any
representation or warranty of Parent or Parent's failure to comply in any
material respect with any of its covenants or agreements, or if any
representation or warranty of Parent or Purchaser shall be or become untrue in
any material respect, which breach or failure to comply or untruth is not
curable or, if curable, is not cured within 30 Business Days (as defined in the
Merger Agreement) after written notice thereof has been given to Parent
(materiality being construed in light of the transactions contemplated by the
Merger Agreement); (f) by Parent prior to the completion of the Offer, upon a
material breach of any representation, or warranty of the Company or the
Company's failure to comply in any material respect with any of its covenants or
agreements, or if any representation or warranty of the Company shall be or
become untrue in any material respect, which breach or failure to comply or
untruth is not curable or, if curable, is not cured within 30 Business Days
after written notice thereof has been given to the Company (materiality being
construed in light of the transactions contemplated by the Merger Agreement); or
(g) by Parent or by the Company, if Common Shares shall not have been purchased
pursuant to the Offer by December 31, 1998 (the "Termination Date"), provided
that such right to terminate the Merger Agreement shall not be available to a
party whose failure to fulfill any obligation under the Merger Agreement has
been the cause of the failure of such purchase to occur by such date.
 
     Fees and Expenses.  The Merger Agreement provides that, if the Merger is
not consummated, all costs and expenses incurred in connection with the Merger
Agreement and the transactions contemplated thereby shall be paid by the party
incurring such costs or expenses, except for expenses incurred in connection
with the printing, mailing and solicitation of proxies from shareholders and all
filing fees and related expenses, which shall be borne equally by Parent and the
Company.
 
     Notwithstanding the foregoing provisions, as described under "Prohibition
on Solicitation", above, if prior to the purchase of Common Shares pursuant to
the Offer, there is an Acquisition Proposal which the Company Board determines
represents a more favorable transaction to the Company and its shareholders than
the transactions contemplated by the Merger Agreement, and if the Company Board,
after consultation with
                                       11
<PAGE>   14
 
outside counsel, shall have determined that failure to terminate the Merger
Agreement is reasonably likely to be inconsistent with the fiduciary duties of
the Company Board under applicable Law, the Company may terminate the Merger
Agreement. If the Company so elects to terminate the Merger Agreement, the
Company shall, immediately prior to any such termination, pay a termination fee,
in the amount of $30 million in immediately available funds, by wire transfer to
a bank account designated by Parent. In the event of a termination by Parent for
a willful breach of a representation or warranty by the Company, the Company
shall pay Parent $10 million in immediately available funds.
 
     The Company will also pay a $30 million termination fee following the
termination of the Merger Agreement by Parent (i) following a withdrawal by the
Company Board of its recommendation that the shareholders approve the Merger
Agreement (other than if the recommendation is withdrawn because the conditions
to the consummation of the Merger cannot be fulfilled for any reason other than
a breach by the Company), or (ii)(A) by virtue of an uncured breach of covenant
by the Company or (B) after the Termination Date, in each case if termination
follows the making of an Acquisition Proposal by a third party, and with the
termination fee payable only upon the execution, within one year of such
termination, of a definitive agreement implementing an Acquisition Proposal.
 
     Amendment.  The Merger Agreement may be amended by the parties thereto at
any time before or after the approval of the Merger Agreement by the
shareholders of the Company, but after such approval no amendment or
modification shall be made which in any way materially adversely affects the
rights of such shareholders without the further approval of such shareholders.
The Merger Agreement may not be amended, modified or supplemented except by
written agreement of the parties thereto.
 
Shareholder Agreement
 
     The Shareholder Agreement dated as of June 3, 1998, by and among Parent,
Purchaser and Allied Mutual with respect to the Common Shares and Preferred
Shares owned by Allied Mutual is summarized below:
 
     Pursuant to the Shareholder Agreement, Allied Mutual agrees to tender, and
not to withdraw, the Common Shares it holds pursuant to the Offer. Allied Mutual
further agrees (i) not to sell, transfer, pledge, assign or otherwise dispose
of, or enter into any Contract (as defined therein), option or other arrangement
(including any profit sharing arrangement) or understanding with respect to the
sale, transfer, pledge, assignment or other disposition of, the Common Shares or
Preferred Shares held by Allied Mutual (collectively, the "Securities") to any
person other than Parent or Parent's designee, (ii) not to enter into any voting
arrangement, whether by proxy, voting agreement, voting, trust,
power-of-attorney or otherwise, with respect to the Securities.
 
     Allied Mutual agrees not to, and agrees not to permit any investment
banker, financial adviser, attorney, accountant or other representative or agent
of Allied Mutual to, directly or indirectly (i) solicit, initiate or knowingly
encourage (including by way of furnishing information), or knowingly facilitate
any inquiries or the making of any proposal which constitutes, or may reasonably
be expected to lead to, any Acquisition Proposal or (ii) participate in any
discussions or negotiations regarding any Acquisition Proposal.
 
     At any meeting of shareholders of the Company called to vote upon the
Merger and the Merger Agreement or at any adjournment thereof or in any other
circumstances upon which a vote, consent or other approval (including by written
consent) with respect to the Merger and the Merger Agreement is sought, Allied
Mutual agrees to, including by initiating a written consent solicitation if
requested by Parent, vote (or cause to be voted) Allied Mutual's Securities in
favor of the Merger, the adoption of the Merger Agreement and the approval of
the other transactions contemplated by the Merger Agreement. At any meeting of
shareholders of the Company or at any adjournment thereof or in any other
circumstances upon which Allied Mutual's vote, consent or other approval is
sought, Allied Mutual will vote (or cause to be voted) Allied Mutual's
Securities against (i) any merger (other than the Merger), consolidation,
combination, sale of substantial assets, reorganization, recapitalization,
dissolution, liquidation or winding up of or by the Company or any other
Acquisition Proposal (collectively, "Alternative Transactions") or (ii) any
amendment of the Company's Certificate of Incorporation or By-laws or other
proposal or transaction involving the Company or
                                       12
<PAGE>   15
 
any of its subsidiaries, which amendment or other proposal or transaction would
in any manner impede, frustrate, prevent or nullify, the Merger, the Merger
Agreement or any of the other transactions contemplated by the Merger Agreement
including any consent to the treatment of any Securities in or in connection
with such transaction (collectively, "Frustrating Transactions").
 
     The Shareholder Agreement terminates upon the earlier of (i) the
termination of the Merger Agreement in accordance with its terms and (ii) the
termination of the Allied Mutual Merger Agreement.
 
     Allied Mutual irrevocably grants to, and appoints, any individual who shall
be designated by Parent as Allied Mutual's proxy and attorney-in-fact (with full
power of substitution), for and in the name, place and stead of Allied Mutual,
to vote Allied Mutual's Securities, or grant a consent or approval in respect of
such Securities, at any meeting of shareholders of the Company or at any
adjournment thereof or in any other circumstances upon which their vote, consent
or other approval is sought, (i) in favor of the Merger, the adoption by the
Company of the Merger Agreement and the approval of the other transactions
contemplated by the Merger Agreement, and (ii) against any Alternative
Transaction or Frustrating Transaction.
 
7. CONDITIONS OF THE OFFER.
 
     The discussion set forth in Section 14 of the Offer to Purchase is hereby
amended and supplemented as follows:
 
     Notwithstanding any other provisions of the Offer, Purchaser shall not be
required to accept for payment or, subject to any applicable rules and
regulations of the SEC, including Rule 14e-1(c) under the Exchange Act (relating
to Purchaser's obligation to pay for or return tendered Common Shares promptly
after termination or withdrawal of the Offer), to pay for Common Shares not
theretofore accepted for payment or paid for (i) unless any one or more of the
Minimum Condition or the Insurance Regulatory Approval Condition has not been
satisfied, and the waiting period under the Hart-Scott-Rodino Antitrust
Improvements Act of 1976, as amended (the "HSR Act"), applicable to the purchase
of Common Shares pursuant to the Offer shall not have expired or been
terminated, or (ii) if at any time on or after the date of the Merger Agreement
and at or before the time that the particular Common Shares are accepted for
payment (whether or not any other Common Shares shall theretofore have been
accepted for payment or paid for pursuant to the Offer) any of the following
conditions exists:
 
          (a) there shall have occurred and be continuing (i) any general
     suspension of, or limitation on prices for, trading in securities on the
     New York Stock Exchange, (ii) a declaration of a banking moratorium or any
     suspension of payments in respect of banks in the United States, or (iii) a
     commencement of a war, armed hostilities or other international or national
     calamity directly involving the United States which has a material adverse
     effect on the general economic conditions in the United States;
 
          (b) any statute, rule, regulation, a temporary, preliminary or
     permanent order or injunction shall be promulgated, enacted, entered,
     enforced or deemed applicable to the Offer, the Merger or performance under
     the Merger Agreement, by any state, federal or foreign government or
     governmental authority or court or governmental agency of competent
     jurisdiction that (i) prohibits the consummation of the Offer or the Merger
     or (ii) imposes material limitations on the ability of Purchaser
     effectively to exercise full rights of ownership with respect to the Common
     Shares, including, without limitation, the right to vote any Common Shares
     purchased by it on all matters properly presented to the stockholders of
     the Company or to operate a material portion of the business of the Company
     and its subsidiaries; provided that Parent and Purchaser shall have used
     their reasonable best efforts to have any such decree, order or injunction
     vacated or reversed;
 
          (c) the Company shall have entered into an agreement obligating the
     Company to accept an Acquisition Proposal (as defined in the Merger
     Agreement) with a person other than Purchaser or an affiliate of either;
 
          (d)(i) the Company shall have breached or failed to perform in any
     material respect any of its material obligations, covenants or agreements
     under the Merger Agreement (materiality being construed
                                       13
<PAGE>   16
 
     in light of the transactions contemplated by the Merger Agreement), (ii)
     the representations and warranties of the Company contained in the Merger
     Agreement shall not be true and correct as of the date of the Merger
     Agreement or as of the scheduled or extended expiration of the Offer, as if
     made as of such dates (provided that representations and warranties made as
     of a specified date prior to the date of the Merger Agreement, need only be
     true as of such date), unless the failure to be so true and correct
     (without regard to any materiality qualifiers) would not, in the aggregate,
     be reasonably likely to have a Material Adverse Effect (as defined in the
     Merger Agreement) or (iii) the representations and warranties of the
     Company contained in Sections 4.2 or 4.4 of the Merger Agreement shall not
     be true and correct in all material respects;
 
          (e) the Company Board shall have withdrawn its recommendation or
     modified its recommendation in a manner adverse to Parent or Purchaser; or
 
          (f) the failure to obtain any Governmental Approvals (as defined in
     the Merger Agreement), which failure, in the aggregate, would reasonably be
     expected to have a Material Adverse Effect.
 
     The foregoing conditions are for the sole benefit of Parent and Purchaser
and may be asserted by Parent or Purchaser in their sole discretion, regardless
of the circumstances giving rise to any such conditions or may be waived by
Parent or Purchaser in whole or in part at any time and from time to time in
their sole discretion (subject to the terms of the Merger Agreement). The
failure by Parent or Purchaser at any time to exercise any of the foregoing
rights shall not be deemed a waiver of any such right, the waiver of any such
right with respect to particular facts and other circumstances shall not be
deemed a waiver with respect to any other facts and circumstances, and each such
right shall be deemed an ongoing right which may be asserted at any time and
from time to time.
 
8. CERTAIN LEGAL MATTERS; REGULATORY APPROVALS; CERTAIN LITIGATION.
 
     The discussion set forth in Section 15 of the Offer to Purchase is hereby
amended and supplemented as follows:
 
     In connection with the execution of the Merger Agreement, Parent and
Purchaser agreed from and after the date of the Merger Agreement and until the
Effective Time, to cease, in any and all respects, the prosecution of any
litigation against the Company or any of its affiliates. In addition, Parent and
Purchaser agreed that immediately following the Effective Time, they would seek
the dismissal, with prejudice, of any and all litigation brought by them against
the Company or any of its affiliates.
 
  Certain Litigation
 
     On December 31, 1997, a complaint was filed by Mary M. Rieff, a
policyholder of Allied Mutual, in the Iowa District Court in and for Polk County
Iowa, against the Company and certain other individuals who are or were officers
and/or directors of Allied Mutual and the Company. The complaint, an alleged
policyholder derivative action brought on behalf of Allied Mutual, asserts,
among other things, (a) that the defendants were responsible for the
inappropriate transfer of Allied Mutual's corporate assets, the seizure of
certain corporate opportunities, and the implementation of an improper de facto
demutualization without informing or compensating policyholders or receiving the
appropriate approval from regulatory authorities; (b) that this allegedly
wrongful demutualization began on or about January 1, 1985 and was accomplished
through transfer of Allied Mutual's assets to the Company and to the individual
defendants for inadequate consideration; (c) that the individual defendants
breached fiduciary duties owed to Allied Mutual, wasted its corporate assets,
and intentionally interfered with its contracts, prospective business advantage,
and business relationships; and (d) that the defendants improperly transferred
substantial ownership of and control over the Company and Allied Mutual's
insurance business. The complaint further asserts that as a result of the
foregoing, Allied Mutual and its policyholders have suffered damages in excess
of $500 million. The complaint requests and accounting of the assets allegedly
wrongfully transferred to the Company and compensation to Allied Mutual for the
value of such assets, for the seizure of corporate opportunities, and for the de
facto demutualization of Allied Mutual. The complaint also asks for certain
other relief, including attorney's fees and costs, equitable relief and
interest, and restitution for any assets wrongfully transferred or conveyed.
                                       14
<PAGE>   17
 
     On June 1, 1998, a motion was filed by Mary M. Rieff seeking to enjoin the
defendant directors of Allied Mutual from considering, negotiating or approving
any transaction on behalf of Allied Mutual with Parent or any third party
because of alleged conflicts of interest of the members of the Board of
Directors of Allied Mutual.
 
     On June 4, 1998, the complaint was amended to include a class action
component.
 
9. MISCELLANEOUS.
 
     Parent and Purchaser have filed with the SEC the Schedule 14D-1, together
with exhibits, pursuant to Rule 14d-3 of the General Rules and Regulations under
the Exchange Act, furnishing certain additional information with respect to the
Offer. The Schedule 14D-1, and any amendments thereto, may be inspected at, and
copies may be obtained from, the same places and in the same manner as set forth
in Section 8 (except that they may not be available at the regional offices of
the SEC).
 
                                    NATIONWIDE GROUP ACQUISITION CORPORATION
 
June 10, 1998
 
                                       15
<PAGE>   18
 
     Facsimile copies of one of the Letters of Transmittal, properly completed
and duly signed, will be accepted. The Letters of Transmittal, certificates for
the Common Shares and any other required documents should be sent by each
shareholder of the Company or his broker, dealer, commercial bank, trust company
or other nominee to the Depositary as follows:
 
                        The Depositary for the Offer is:
 
                    CHASEMELLON SHAREHOLDER SERVICES, L.L.C.
 
<TABLE>
<S>                                      <C>                                      <C>
              By Mail:                      By Overnight Courier Delivery:                      By Hand:
        Post Office Box 3301                  85 Challenger Road -- Mail                120 Broadway, 13th Floor
     South Hackensack, NJ 07606                      Drop - Reorg                          New York, NY 10271
        Attn: Reorganization                   Ridgefield Park, NJ 07660                  Attn: Reorganization
             Department                          Attn: Reorganization                          Department
                                                      Department
</TABLE>
 
                           By Facsimile Transmission:
                                 (201) 329-8936
                             Confirm by Telephone:
                                 (201) 296-4860
 
     Any questions or requests for assistance may be directed to the Information
Agent or the Dealer Manager at their respective telephone numbers and locations
listed below. Additional copies of the Offer to Purchase, this Supplement, the
revised Letter of Transmittal and the revised Notice of Guaranteed Delivery may
be obtained from the Information Agent at its address and telephone numbers set
forth below. Holders of Common Shares may also contact their broker, dealer,
commercial bank or trust company or other nominee for assistance concerning the
Offer.
 
                    The Information Agent for the Offer is:
 
                            GEORGESON & COMPANY INC.
 
                               Wall Street Plaza
                               New York, NY 10005
                Bankers and Brokers call collect: (212) 440-9800
                   All Others Call Toll-Free: (800) 223-2064
               INTERNET: World Wide Web http://www.georgeson.com
 
                      The Dealer Manager for the Offer is:
 
                     CREDIT SUISSE FIRST BOSTON CORPORATION
 
                             Eleven Madison Avenue
                               New York, NY 10010
                         Call Toll Free: (800) 863-6558

<PAGE>   1

                                                               Exhibit (a)(29)
 

                             LETTER OF TRANSMITTAL
                        TO TENDER SHARES OF COMMON STOCK
 
                                       OF
 
                               ALLIED GROUP, INC.
              PURSUANT TO THE OFFER TO PURCHASE DATED MAY 19, 1998
                 AND THE SUPPLEMENT THERETO DATED JUNE 10, 1998
 
                                       BY
 
                    NATIONWIDE GROUP ACQUISITION CORPORATION
                          A WHOLLY OWNED SUBSIDIARY OF
 
                      NATIONWIDE MUTUAL INSURANCE COMPANY
 
           THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M.,
 NEW YORK CITY TIME, ON MONDAY, AUGUST 31, 1998, UNLESS THE OFFER IS EXTENDED.
 
                        The Depositary for the Offer is:
 
                    CHASEMELLON SHAREHOLDER SERVICES, L.L.C.
 
<TABLE>
<S>                                <C>                                <C>
             By Mail:                By Overnight Courier Delivery:                By Hand:
       Post Office Box 3301            85 Challenger Road -- Mail          120 Broadway, 13th Floor
    South Hackensack, NJ 07606                Drop - Reorg                    New York, NY 10271
 Attn: Reorganization Department       Ridgefield Park, NJ 07660       Attn: Reorganization Department
                                    Attn: Reorganization Department
</TABLE>
 
                           By Facsimile Transmission:
                                 (201) 329-8936
                             Confirm by Telephone:
                                 (201) 296-4860
 
    DELIVERY OF THIS REVISED LETTER OF TRANSMITTAL TO AN ADDRESS OTHER THAN AS
SET FORTH ABOVE OR TRANSMISSION OF INSTRUCTIONS VIA FACSIMILE TRANSMISSION OTHER
THAN AS SET FORTH ABOVE WILL NOT CONSTITUTE A VALID DELIVERY.
 
    YOU MUST SIGN THIS REVISED LETTER OF TRANSMITTAL WHERE INDICATED BELOW AND
COMPLETE THE SUBSTITUTE FORM W-9 PROVIDED BELOW. THE INSTRUCTIONS ACCOMPANYING
THIS REVISED LETTER OF TRANSMITTAL SHOULD BE READ CAREFULLY BEFORE COMPLETING
THIS REVISED LETTER OF TRANSMITTAL.
<PAGE>   2
 
- --------------------------------------------------------------------------------
                     DESCRIPTION OF COMMON SHARES TENDERED
 
<TABLE>
<CAPTION>
<S>                                                   <C>                    <C>                  <C>
- -----------------------------------------------------
   NAME(S) AND ADDRESS(ES) OF REGISTERED OWNER(S)                    COMMON SHARE CERTIFICATE(S) AND
    (PLEASE FILL IN, IF BLANK, EXACTLY AS NAME(S)                        COMMON SHARES TENDERED
      APPEAR(S) ON COMMON SHARE CERTIFICATE(S))                   (ATTACH ADDITIONAL LIST IF NECESSARY)
- -------------------------------------------------------------------------------------------------------------------
                                                                                 TOTAL NUMBER
                                                                               OF COMMON SHARES
                                                           COMMON SHARE         REPRESENTED BY
                                                           CERTIFICATE           COMMON SHARE     NUMBER OF COMMON
                                                            NUMBER(S)*         CERTIFICATE(S)*    SHARES TENDERED**
                                                       ----------------------------------------------------------
                                                       ----------------------------------------------------------
                                                       ----------------------------------------------------------
                                                       ----------------------------------------------------------
                                                       ----------------------------------------------------------
                                                       ----------------------------------------------------------
                                                        TOTAL NUMBER OF
                                                         COMMON SHARES
- -------------------------------------------------------------------------------------------------------------------
  * Need not be completed by shareholders delivering Common Shares by book-entry transfers.
 ** Unless otherwise indicated, it will be assumed that all Common Shares evidenced by each Common Share
    Certificate delivered to the Depositary are being tendered hereby. See Instruction 4.
- -------------------------------------------------------------------------------------------------------------------
</TABLE>
<PAGE>   3
 
     This revised Letter of Transmittal is to be completed by shareholders
either if certificates ("Common Share Certificates") evidencing shares of common
stock, no par value, of Allied Group, Inc. ("Common Shares") are to be forwarded
herewith or, unless an Agent's Message (as defined below) is utilized, if
delivery of Common Shares is to be made by book-entry transfer to the
Depositary's account at The Depository Trust Company or Philadelphia Depository
Trust Company (each a "Book-Entry Transfer Facility" and collectively, the
"Book-Entry Transfer Facilities") pursuant to the book-entry transfer procedure
described in "Procedures for Tendering Common Shares" of the Offer to Purchase
(as defined below) as supplemented by Section 2 of the Supplement (as defined
below). DELIVERY OF DOCUMENTS TO A BOOK-ENTRY TRANSFER FACILITY DOES NOT
CONSTITUTE DELIVERY TO THE DEPOSITARY.
 
     Shareholders who have previously tendered Common Shares pursuant to the
Offer using the previously circulated Letter of Transmittal or the Notice of
Guaranteed Delivery and who have not properly withdrawn such Common Shares have
validly tendered such Common Shares for the purposes of the Offer, as amended,
and need not take any further action.
 
     Shareholders whose Common Share Certificates are not immediately available
or who cannot deliver all documents required hereby to the Depositary prior to
the Expiration Date (as defined in Section 1 of the Supplement) or who cannot
complete the procedure for delivery by book-entry transfer on a timely basis and
who wish to tender their Common Shares must do so pursuant to the guaranteed
delivery procedure described in "Procedures for Tendering Common Shares" of the
Offer to Purchase as supplemented by Section 2 of the Supplement. See
Instruction 2.
 
[ ] CHECK HERE IF TENDERED COMMON SHARES ARE BEING DELIVERED BY BOOK-ENTRY
    TRANSFER TO THE DEPOSITARY'S ACCOUNT AT ONE OF THE BOOK-ENTRY TRANSFER
    FACILITIES AND COMPLETE THE FOLLOWING.
 
   Name of Tendering Institution________________________________________________
 
   Check Box of Applicable Book-Entry Transfer Facility:
 
<TABLE>
<CAPTION>
                                                                  PHILADELPHIA
                                                 THE DEPOSITORY    DEPOSITORY
                                                 TRUST COMPANY    TRUST COMPANY
                                                 --------------   -------------
   <S>                                           <C>              <C>
   (CHECK ONE)                                         [ ]              [ ]
</TABLE>
 
   Account Number______________________________________________________________
 
   Transaction Code Number_____________________________________________________
 
[ ] CHECK HERE IF TENDERED COMMON SHARES ARE BEING TENDERED PURSUANT TO A NOTICE
    OF GUARANTEED DELIVERY PREVIOUSLY SENT TO THE DEPOSITARY AND COMPLETE THE
    FOLLOWING.
 
   Name(s) of Registered Holder(s)______________________________________________
 
   Window Ticket No. (if any)___________________________________________________
 
   Date of Execution of Notice of Guaranteed Delivery___________________________
 
   Name of Institution which Guaranteed Delivery________________________________
 
     The names and addresses of the registered holders should be printed, if not
already printed above, exactly as they appear on the certificates representing
Common Shares tendered hereby. The certificates and number of Common Shares that
the undersigned wishes to tender should be indicated in the appropriate boxes.
 
[ ] CHECK HERE IF TENDER IS BEING MADE PURSUANT TO LOST, STOLEN, DESTROYED OR
    MUTILATED SECURITIES. SEE INSTRUCTION 11.
 
                   NOTE: SIGNATURE(S) MUST BE PROVIDED BELOW.
                 PLEASE READ THE INSTRUCTIONS SET FORTH IN THIS
                    REVISED LETTER OF TRANSMITTAL CAREFULLY.
 
                                        2
<PAGE>   4
 
Ladies and Gentlemen:
 
     The undersigned hereby tenders to Nationwide Group Acquisition Corporation
("Purchaser"), an Ohio corporation and a wholly owned subsidiary of Nationwide
Mutual Insurance Company ("Parent"), an Ohio mutual insurance company, the
above-described shares of common stock, no par value (the "Common Shares") of
Allied Group, Inc., an Iowa corporation (the "Company"), pursuant to Purchaser's
offer to purchase all outstanding Common Shares, at a price of $48.25 per share,
net to the seller in cash, without interest thereon, upon the terms and subject
to the conditions set forth in the Offer to Purchase, dated May 19, 1998 (the
"Offer to Purchase"), the Supplement thereto, dated June 10, 1998 (the
"Supplement"), receipt of which is hereby acknowledged, and in this revised
Letter of Transmittal (which, as amended from time to time, together constitute
the "Offer"). The undersigned understands that Purchaser reserves the right to
transfer or assign, in whole or in part from time to time, to one or more of its
affiliates, the right to purchase all or any portion of the Common Shares
tendered pursuant to the Offer.
 
     Subject to, and effective upon, acceptance for payment of the Common Shares
tendered herewith, in accordance with the terms of the Offer (including, if the
Offer is extended or amended, the terms and conditions of such extension or
amendment), the undersigned hereby sells, assigns and transfers to, or upon the
order of, Purchaser all right, title and interest in and to all the Common
Shares that are being tendered hereby and all dividends, distributions
(including, without limitation, distributions of additional Common Shares) and
rights declared, paid or distributed in respect of such Common Shares on or
after May 18, 1998 (collectively, "Distributions"), and irrevocably appoints
ChaseMellon Shareholder Services, L.L.C., (the "Depositary") the true and lawful
agent and attorney-in-fact of the undersigned with respect to such Common Shares
and all Distributions, with full power of substitution (such power of attorney
being deemed to be an irrevocable power coupled with an interest), to (i)
deliver Common Share Certificates evidencing such Common Shares and all
Distributions, or transfer ownership of such Common Shares and all Distributions
on the account books maintained by a Book-Entry Transfer Facility, together, in
either case, with all accompanying evidences of transfer and authenticity, to or
upon the order of Purchaser, (ii) present such Common Shares and all
Distributions for transfer on the books of the Company and (iii) receive all
benefits and otherwise exercise all rights of beneficial ownership of such
Common Shares and all Distributions, all in accordance with the terms of the
Offer.
 
     If, on or after the date of the Offer to Purchase, the Company should
declare or pay any dividend on the Common Shares, other than regular quarterly
dividends, or make any distribution (including, without limitation, the issuance
of additional Common Shares pursuant to a stock dividend or stock split, the
issuance of other securities or the issuance of rights for the purchase of any
securities) with respect to the Common Shares that is payable or distributable
to shareholders of record on a date prior to the transfer to the name of
Purchaser or its nominee or transferee on the Company's stock transfer records
of the Common Shares purchased pursuant to the Offer, then, without prejudice to
Purchaser's rights under Sections 1 and 14 of the Offer to Purchase and Sections
1 and 7 of the Supplement, (i) the purchase price per Common Share payable by
Purchaser pursuant to the Offer will be reduced by the amount of any such cash
dividend or cash distribution and (ii) any such non-cash dividend, distribution
or right to be received by the tendering shareholders will be received and held
by such tendering shareholders for the account of Purchaser and will be required
to be promptly remitted and transferred by each such tendering shareholder to
the Depositary for the account of Purchaser, accompanied by appropriate
documentation of transfer. Pending such remittance and subject to applicable
law, Purchaser will be entitled to all rights and privileges as owner of any
such non-cash dividend, distribution or right and may withhold the entire
purchase price or deduct from the purchase price the amount or value thereof, as
determined by Purchaser in its sole discretion.
 
     By executing this revised Letter of Transmittal, the undersigned hereby
irrevocably appoints David A. Diamond, W. Sidney Druen and Mark B. Koogler, and
each of them, as the attorneys and proxies of the undersigned, each with full
power of substitution, to the full extent of the undersigned's rights with
respect to the Common Shares tendered by the undersigned and accepted for
payment by Purchaser (and any and all Distributions). All such proxies shall be
considered coupled with an interest in the tendered Common Shares. This
appointment will be effective if, when, and only to the extent that Purchaser
accepts such Common Shares for payment pursuant to the Offer. Upon such
acceptance for payment, all prior proxies given by the undersigned with respect
to such Common Shares, Distributions and other securities will, without further
action, be revoked, and no subsequent proxies may be given. The individuals
named above as proxies will, with respect to the Common Shares, Distributions
and other securities for which the
 
                                        3
<PAGE>   5
 
appointment is effective, be empowered to exercise all voting and other rights
of the undersigned as they, in their sole discretion, may deem proper at any
annual, special, adjourned or postponed meeting of Company shareholders, by
written consent or otherwise, and Purchaser reserves the right to require that,
in order for Common Shares, Distributions or other securities to be deemed
validly tendered, immediately upon Purchaser's acceptance for payment of such
Common Shares, Purchaser or Purchaser's designees must be able to exercise full
voting rights with respect to such Common Shares.
 
     The undersigned hereby represents and warrants that the undersigned has
full power and authority to tender, sell, assign and transfer the Common Shares
tendered hereby and all Distributions, that the undersigned own(s) the Common
Shares tendered hereby within the meaning of Rule 14e-4 promulgated under the
Securities Exchange Act of 1934, as amended ("Rule 14e-4"), that such tender of
Common Shares complies with Rule 14e-4 and that when such Common Shares are
accepted for payment by Purchaser, Purchaser will acquire good, marketable and
unencumbered title thereto and to all Distributions, free and clear of all
liens, restrictions, charges and encumbrances, and that none of such Common
Shares and Distributions will be subject to any adverse claim. The undersigned,
upon request, shall execute and deliver all additional documents deemed by the
Depositary or Purchaser to be necessary or desirable to complete the sale,
assignment and transfer of the Common Shares tendered hereby and all
Distributions. In addition, the undersigned shall remit and transfer promptly to
the Depositary for the account of Purchaser all Distributions in respect of the
Common Shares tendered hereby, accompanied by appropriate documentation of
transfer, and, pending such remittance and transfer or appropriate assurance
thereof, Purchaser shall be entitled to all rights and privileges as owner of
each such Distribution and may withhold the entire purchase price of the Common
Shares tendered hereby, or deduct from such purchase price, the amount or value
of such Distribution as determined by Purchaser in its sole discretion.
 
     No authority herein conferred or agreed to be conferred shall be affected
by, and all such authority shall survive, the death or incapacity of the
undersigned. All obligations of the undersigned hereunder shall be binding upon
the heirs, executors, personal and legal representatives, administrators,
trustees in bankruptcy, successors and assigns of the undersigned. Except as
stated in the Offer to Purchase, this tender is irrevocable.
 
     The undersigned understands that tenders of Common Shares pursuant to any
one of the procedures described in "Procedures for Tendering Common Shares" of
the Offer to Purchase as supplemented by Section 2 of the Supplement and in the
instructions hereto will constitute the undersigned's acceptance of the terms
and conditions of the Offer. Purchaser's acceptance for payment of Common Shares
tendered pursuant to the Offer will constitute a binding agreement between the
undersigned and Purchaser upon the terms and subject to the conditions of the
Offer. The undersigned recognizes that under certain circumstances set forth in
the Offer to Purchase and the Supplement, Purchaser may not be required to
accept for payment any of the Common Shares tendered hereby.
 
     Unless otherwise indicated herein in the box entitled "Special Payment
Instructions," please issue the check for the purchase price and/or return any
Common Share Certificates evidencing Common Shares not tendered or accepted for
payment, in the name(s) of the registered holder(s) appearing above under
"Description of Common Shares Tendered." Similarly, unless otherwise indicated
in the box entitled "Special Delivery Instructions," please mail the check for
the purchase price of all Common Shares purchased and all Common Share
Certificates evidencing Common Shares not tendered or not purchased (and
accompanying documents, as appropriate) to the address(es) of the registered
holder(s) appearing above under "Description of Common Shares Tendered." In the
event that the boxes entitled "Special Payment Instructions" and "Special
Delivery Instructions" are both completed, please issue the check for the
purchase price and/or return any Common Share Certificates for Common Shares not
purchased or not tendered or accepted for payment in the name(s) of, and mail
such check and/or return such Common Share Certificates to, the person(s) so
indicated. Unless otherwise indicated herein in the box entitled "Special
Payment Instructions," please credit any Common Shares tendered hereby and
delivered by book-entry transfer, but which are not purchased, by crediting the
account at the Book-Entry Transfer Facility designated above. The undersigned
recognizes that Purchaser has no obligation, pursuant to the instructions in the
box entitled "Special Payment Instructions," to transfer any Common Shares from
the name of the registered holder(s) thereof if Purchaser does not purchase any
of the Common Shares tendered hereby.
 
                                        4
<PAGE>   6
 
- ------------------------------------------------------------
 
                          SPECIAL PAYMENT INSTRUCTIONS
                        (SEE INSTRUCTIONS 1, 5, 6 AND 7)
        To be completed ONLY if the check for the purchase price of Common
   Shares or Common Share Certificates evidencing Common Shares not tendered
   or not purchased are to be issued in the name of someone other than the
   undersigned, or if the Common Shares delivered by book-entry transfer
   which are not purchased are to be returned by credit to an account
   maintained at a Book-Entry Transfer Facility other than that designated
   above.
 
   Issue [ ] Check [ ] Common Share Certificate to:
 
   Name
   -----------------------------------------------------
                                 (PLEASE PRINT)
 
   Address:
   --------------------------------------------------
 
   ------------------------------------------------------------
                               (INCLUDE ZIP CODE)
 
   ------------------------------------------------------------
         RECIPIENT'S TAXPAYER IDENTIFICATION OR SOCIAL SECURITY NUMBER
                   (ALSO COMPLETE SUBSTITUTE FORM W-9 BELOW)
 
   [ ] Credit unpurchased Common Shares delivered by book-entry transfer to
       the Book-Entry Transfer Facility account set forth below:
 
      Check appropriate box:
        [ ] The Depository Trust Company
        [ ] Philadelphia Depository Trust Company
 
   ------------------------------------------------------------
                                (ACCOUNT NUMBER)
============================================================
 
                         SPECIAL DELIVERY INSTRUCTIONS
                        (SEE INSTRUCTIONS 1, 5, 6 AND 7)
 
        To be completed ONLY if Common Share Certificates tendered and/or
   Common Share Certificates evidencing Common Shares not tendered or not
   purchased are to be mailed to someone other than the undersigned, or to
   the undersigned at an address other than that shown under "Description of
   Common Shares Tendered."
 
   Mail [ ] Check [ ] Common Share Certificates to:
 
   Name:
   -----------------------------------------------------
                                 (PLEASE PRINT)
 
   Address:
   --------------------------------------------------
 
   ------------------------------------------------------------
                               (INCLUDE ZIP CODE)
 
   ------------------------------------------------------------
         RECIPIENT'S TAXPAYER IDENTIFICATION OR SOCIAL SECURITY NUMBER
                   (ALSO COMPLETE SUBSTITUTE FORM W-9 BELOW)
- ------------------------------------------------------------
 
                                        5
<PAGE>   7
 
                                   IMPORTANT
 
                            SHAREHOLDERS: SIGN HERE
             (PLEASE COMPLETE SUBSTITUTE FORM W-9 INCLUDED HEREIN)
 
- --------------------------------------------------------------------------------
 
- --------------------------------------------------------------------------------
                          (SIGNATURE(S) OF HOLDER(S))
Dated:                         1998 
      -------------------------
 
(Must be signed by registered holder(s) exactly as name(s) appear(s) on Common
Share Certificate(s) or on a security position listing or by person(s)
authorized to become registered holder(s) by certificates and documents
transmitted herewith. If signature is by trustees, executors, administrators,
guardians, attorneys-in-fact, officers of corporations or other persons acting
in a fiduciary or representative capacity, please provide the following
information. See Instruction 5.)
 
Name(s):
- --------------------------------------------------------------------------------
 
- --------------------------------------------------------------------------------
                                 (PLEASE PRINT)
Capacity (full title):
- --------------------------------------------------------------------------------
Address:
================================================================================
                               (INCLUDE ZIP CODE)
Daytime Area Code and Telephone No.:
                                    --------------------------------------------
Taxpayer Identification or Social Security No.:
                                               ---------------------------------
                                       (COMPLETE SUBSTITUTE FORM W-9 INCLUDED
                                                            HEREIN)
 
                           GUARANTEE OF SIGNATURE(S)
                           (SEE INSTRUCTIONS 1 AND 5)
Authorized Signature:
                     -----------------------------------------------------------
Name:
     ---------------------------------------------------------------------------
                             (PLEASE TYPE OR PRINT)
Title:
      --------------------------------------------------------------------------
Name of Firm:
             -------------------------------------------------------------------
Address:
        ------------------------------------------------------------------------
                               (INCLUDE ZIP CODE)
Area Code and Telephone No.:
                            ---------------------------------------------------
Dated:                    1998
      ------------------
 
                     FOR USE BY FINANCIAL INSTITUTIONS ONLY
        FINANCIAL INSTITUTIONS: PLACE MEDALLION GUARANTEE IN SPACE BELOW
 
                                        6
<PAGE>   8
 
                                  INSTRUCTIONS
 
             FORMING PART OF THE TERMS AND CONDITIONS OF THE OFFER
 
     1. Guarantee of Signatures.  Except as otherwise provided below, all
signatures on this revised Letter of Transmittal must be guaranteed by a firm
which is a bank, broker, dealer, credit union, savings association or other
entity that is a member in good standing of the Securities Transfer Agents
Medallion Program, the New York Stock Exchange Medallion Signature Guarantee
Program or the Stock Exchange Medallion Program (each, an "Eligible
Institution"). No signature guarantee is required on this Letter of Transmittal
(i) if this Letter of Transmittal is signed by the registered holder(s) (which
term, for purposes of this document, shall include any participant in a
Book-Entry Transfer Facility whose name appears on a security position listing
as the owner of Common Shares) of Common Shares tendered herewith, unless such
holder(s) has (have) completed either the box entitled "Special Payment
Instructions" or the box entitled "Special Delivery Instructions" herein or (ii)
if such Common Shares are tendered for the account of an Eligible Institution.
See Instruction 5.
 
     2. Delivery of Letter of Transmittal and Common Share Certificates.  This
revised Letter of Transmittal is to be used either if Common Share Certificates
are to be forwarded herewith or if Common Shares are to be delivered by
book-entry transfer pursuant to the procedure set forth in "Procedures for
Tendering Common Shares" of the Offer to Purchase as supplemented by Section 2
of the Supplement. Common Share Certificates evidencing all tendered Common
Shares, or confirmation of a book-entry transfer of such Common Shares into the
Depositary's account at one of the Book-Entry Transfer Facilities pursuant to
the procedures set forth in "Procedures for Tendering Common Shares" of the
Offer to Purchase as supplemented by Section 2 of the Supplement, together with
a properly completed and duly executed revised Letter of Transmittal (or
facsimile thereof) with any required signature guarantees (or, in the case of a
book-entry transfer, an Agent's Message) and any other documents required by
this revised Letter of Transmittal, must be received by the Depositary at one of
its addresses set forth herein prior to the Expiration Date. If Common Share
Certificates are forwarded to the Depositary in multiple deliveries, a properly
completed and duly executed Letter of Transmittal must accompany each such
delivery.
 
     Shareholders whose Common Share Certificates are not immediately available,
who cannot deliver their Common Share Certificates and all other required
documents to the Depositary prior to the Expiration Date or who cannot complete
the procedure for delivery by book-entry transfer on a timely basis may tender
their Common Shares pursuant to the guaranteed delivery procedure described in
"Procedures for Tendering Common Shares" of the Offer to Purchase as
supplemented by Section 2 of the Supplement. Pursuant to such procedure: (i)
such tender must be made by or through an Eligible Institution; (ii) a properly
completed and duly executed Notice of Guaranteed Delivery, substantially in the
form provided by Purchaser herewith, must be received by the Depositary prior to
the Expiration Date; and (iii) the Common Share Certificates, in proper form for
transfer, or a confirmation of a book-entry transfer of such Common Shares into
the Depositary's account at one of the Book-Entry Transfer Facilities, together
with a properly completed and duly executed revised Letter of Transmittal (or
manually signed facsimile thereof) with any required signature guarantees (or,
in the case of a book-entry transfer, an Agent's Message), and any other
documents required by this revised Letter of Transmittal, must be received by
the Depositary within three (3) New York Stock Exchange Inc. trading days after
the date of execution of the Notice of Guaranteed Delivery, all as described in
"Procedures for Tendering Common Shares" of the Offer to Purchase.
 
     The term "Agent's Message" means a message, transmitted by a Book-Entry
Transfer Facility to, and received by, the Depositary and forming a part of a
Book-Entry Confirmation (as defined in the Offer to Purchase), which states that
such Book-Entry Transfer Facility has received an express acknowledgment from
the participant in such Book-Entry Transfer Facility tendering the Common Shares
that such participant has received and agrees to be bound by the terms of this
Letter of Transmittal and that Purchaser may enforce such agreement against the
participant.
 
     THE METHOD OF DELIVERY OF THIS REVISED LETTER OF TRANSMITTAL, COMMON SHARE
CERTIFICATES AND ALL OTHER REQUIRED DOCUMENTS, INCLUDING DELIVERY THROUGH ANY
BOOK-ENTRY TRANSFER FACILITY, IS AT THE SOLE OPTION AND RISK OF THE TENDERING
SHAREHOLDER, AND THE DELIVERY WILL BE DEEMED
 
                                        7
<PAGE>   9
 
MADE ONLY WHEN ACTUALLY RECEIVED BY THE DEPOSITARY. IF DELIVERY IS BY MAIL,
REGISTERED MAIL WITH RETURN RECEIPT REQUESTED, PROPERLY INSURED, IS RECOMMENDED.
IN ALL CASES, SUFFICIENT TIME SHOULD BE ALLOWED TO ENSURE TIMELY DELIVERY.
 
     No alternative, conditional or contingent tenders will be accepted and no
fractional Common Shares will be purchased. By execution of this revised Letter
of Transmittal (or a facsimile hereof), all tendering shareholders waive any
right to receive any notice of the acceptance of their Common Shares for
payment.
 
     3. Inadequate Space.  If the space provided herein under "Description of
Common Shares Tendered" is inadequate, the Common Share Certificate number, the
total number of Common Shares represented by such Common Share Certificates and
the number of Common Shares tendered should be listed on a separate schedule and
attached hereto.
 
     4. Partial Tenders (not applicable to shareholders who tender by book-entry
transfer).  If fewer than all the Common Shares evidenced by any Common Share
Certificate delivered to the Depositary herewith are to be tendered hereby, fill
in the number of shares of Common Shares which are to be tendered in the column
entitled "Number of Common Shares Tendered" in the above "Description of Common
Shares Tendered". In such cases, new Common Share Certificate(s) evidencing the
remainder of the Common Shares that were evidenced by the Common Share
Certificate(s) delivered to the Depositary herewith will be sent to the
person(s) signing this revised Letter of Transmittal, unless otherwise provided
in the box entitled "Special Delivery Instructions," as soon as practicable
after the expiration or termination of the Offer. All Common Shares evidenced by
Common Share Certificates delivered to the Depositary will be deemed to have
been tendered unless otherwise indicated.
 
     5. Signatures on Revised Letter of Transmittal; Stock Powers and
Endorsements.  If this revised Letter of Transmittal is signed by the registered
holder(s) of the Common Shares tendered hereby, the signature(s) must correspond
exactly with the name(s) as written on the face of the Common Share
Certificate(s) evidencing such Common Shares without alteration, enlargement or
any other change whatsoever. DO NOT SIGN THE BACK OF THE COMMON SHARE
CERTIFICATES.
 
     If any Common Shares tendered hereby are owned of record by two or more
persons, all such persons must sign this revised Letter of Transmittal.
 
     If any of the Common Shares tendered hereby are registered in the names of
different holders, it will be necessary to complete, sign and submit as many
separate revised Letters of Transmittal as there are different registrations of
such Common Shares.
 
     If this revised Letter of Transmittal is signed by the registered holder(s)
of the Common Shares tendered hereby, no endorsements of Common Share
Certificates or separate stock powers are required, unless payment is to be made
to, or Common Share Certificates evidencing Common Shares not tendered or not
purchased are to be issued in the name of, a person other than the registered
holder(s), in which case, the Common Share Certificate(s) evidencing the Common
Shares tendered hereby must be endorsed or accompanied by appropriate stock
powers, in either case signed exactly as the name(s) of the registered holder(s)
appear(s) on such Common Share Certificate(s). Signatures on such Common Share
Certificate(s) and stock powers must be guaranteed by an Eligible Institution.
 
     If this revised Letter of Transmittal is signed by a person other than the
registered holder(s) of the Common Shares tendered hereby, the Common Share
Certificate(s) evidencing the Common Shares tendered hereby must be endorsed or
accompanied by appropriate stock powers, in either case signed exactly as the
name(s) of the registered holder(s) appear(s) on such Common Share
Certificate(s). Signatures on such Common Share Certificate(s) and stock powers
must be guaranteed by an Eligible Institution.
 
     If this revised Letter of Transmittal or any Common Share Certificates or
stock power is signed by a trustee, executor, administrator, guardian,
attorney-in-fact, officer of a corporation or other person acting in a fiduciary
or representative capacity, such person should so indicate when signing, and
proper evidence satisfactory to Purchaser of such person's authority so to act
must be submitted.
 
                                        8
<PAGE>   10
 
     6. Stock Transfer Taxes.  Except as otherwise provided in this Instruction
6, Purchaser will pay all stock transfer taxes with respect to the sale and
transfer of any Common Shares to it or its order pursuant to the Offer. If,
however, payment of the purchase price of any Common Shares purchased is to be
made to, or Common Share Certificate(s) evidencing Common Shares not tendered or
not purchased are to be issued in the name of, a person other than the
registered holder(s), the amount of any stock transfer taxes (whether imposed on
the registered holder(s), such other person or otherwise) payable on account of
the transfer to such other person will be deducted from the purchase price of
such Common Shares purchased, unless evidence satisfactory to Purchaser of the
payment of such taxes, or exemption therefrom, is submitted. Except as provided
in this Instruction 6, it will not be necessary for transfer tax stamps to be
affixed to the Common Share Certificates evidencing the Common Shares tendered
hereby.
 
     7. Special Payment and Delivery Instructions.  If a check for the purchase
price of any Common Shares tendered hereby is to be issued, or Common Share
Certificate(s) evidencing Common Shares not tendered or not purchased are to be
issued, in the name of a person other than the person(s) signing this revised
Letter of Transmittal or if such check or any such Common Share Certificate is
to be sent to someone other than the person(s) signing this revised Letter of
Transmittal or to the person(s) signing this revised Letter of Transmittal but
at an address other than that shown in the box entitled "Description of Common
Shares Tendered," the appropriate boxes on this revised Letter of Transmittal
must be completed. Shareholders tendering Common Shares by book-entry transfer
may request that Common Shares not purchased be credited to such account
maintained at a Book-Entry Transfer Facility as such stockholder may designate
in the box entitled "Special Payment Instructions" hereof. If no such
instructions are given, all such Common Shares not purchased will be returned by
crediting the account at the Book-Entry Transfer Facilities designated herein as
the account from which such Common Shares were delivered.
 
     8. Waiver of Conditions.  The conditions of the Offer may be waived, in
whole or in part, by Purchaser, in its sole discretion, at any time and from
time to time, in the case of any Common Shares tendered.
 
     9. Questions and Requests for Assistance or Additional Copies.  Questions
and requests for assistance may be directed to the Information Agent or Dealer
Manager at their respective addresses or telephone numbers set forth below.
Additional copies of the Offer to Purchase, the Supplement, this revised Letter
of Transmittal and other tender offer materials may be obtained from the
Information Agent or the Dealer Manager, and copies will be furnished promptly
at Purchaser's expense. No fees or commissions will be paid to brokers, dealers
or other persons (other than the Information Agent and the Dealer Manager) for
soliciting tenders of Common Shares pursuant to the Offer.
 
     10. Substitute Form W-9.  Each tendering shareholder is required to provide
the Depositary with a correct Taxpayer Identification Number ("TIN") on the
Substitute Form W-9 which is provided under "Important Tax Information" below,
and to certify, under penalties of perjury, that such number is correct and that
such shareholder is not subject to backup withholding of federal income tax. If
a tendering shareholder has been notified by the Internal Revenue Service that
such shareholder is subject to backup withholding, such shareholder must cross
out item (2) of the Certification box of the Substitute Form W-9, unless such
shareholder has since been notified by the Internal Revenue Service that such
shareholder is no longer subject to backup withholding. Failure to provide the
information on the Substitute Form W-9 may subject the tendering shareholder to
31% federal income tax withholding on the payment of the purchase price of all
Common Shares purchased from such shareholder. If the tendering shareholder has
not been issued a TIN and has applied for one or intends to apply for one in the
near future, such shareholder should write "Applied For" in the space provided
for the TIN in Part 1 of the Substitute Form W-9, and sign and date the
Substitute Form W-9. If "Applied For" is written in Part 1 and the Depositary is
not provided with a TIN within 60 days, the Depositary will withhold 31% on all
payments of the purchase price to such shareholder until a TIN is provided to
the Depositary.
 
     11. Lost, Stolen, Destroyed or Mutilated Common Share Certificates.  If any
Common Share Certificates have been lost, destroyed, mutilated or stolen, the
shareholder should promptly notify the Depositary. The shareholder will then be
instructed as to the steps that must be taken in order to replace the Common
Share Certificate(s). This revised Letter of Transmittal and related documents
cannot be
 
                                        9
<PAGE>   11
 
processed until the procedures for replacing lost or destroyed Common Share
Certificates have been followed. In order to facilitate replacement, contact
Harris Trust & Savings Bank at (312) 360-5100.
 
     IMPORTANT: THIS REVISED LETTER OF TRANSMITTAL (OR FACSIMILE HEREOF),
PROPERLY COMPLETED AND DULY EXECUTED (TOGETHER WITH ANY REQUIRED SIGNATURE
GUARANTEES AND COMMON SHARE CERTIFICATES OR CONFIRMATION OF BOOK-ENTRY TRANSFER
AND ALL OTHER REQUIRED DOCUMENTS) OR A PROPERLY COMPLETED AND DULY EXECUTED
NOTICE OF GUARANTEED DELIVERY, MUST BE RECEIVED BY THE DEPOSITARY PRIOR TO THE
EXPIRATION DATE.
 
                           IMPORTANT TAX INFORMATION
 
     Under the federal income tax law, a shareholder whose tendered Common
Shares are accepted for payment is required by law to provide the Depositary (as
payer) with such shareholder's correct TIN on Substitute Form W-9 below. If such
shareholder is an individual, the TIN is such shareholder's social security
number. If the Depositary is not provided with the correct TIN, the shareholder
may be subject to a $50 penalty imposed by the Internal Revenue Service and
payments that are made to such shareholder with respect to Common Shares
purchased pursuant to the Offer may be subject to backup withholding of 31%. In
addition, if a shareholder makes a false statement that results in no imposition
of backup withholding, and there was no reasonable basis for such a statement, a
$500 penalty may also be imposed by the Internal Revenue Service.
 
     Certain shareholders (including, among others, all corporations and certain
foreign individuals) are not subject to these backup withholding and reporting
requirements. In order for a foreign individual to qualify as an exempt
recipient, such individual must submit a statement, signed under penalties of
perjury, attesting to such individual's exempt status. Forms of such statements
can be obtained from the Depositary. See the enclosed Guidelines for
Certification of Taxpayer Identification Number on Substitute Form W-9 for
additional instructions. A shareholder should consult his or her tax advisor as
to such shareholder's qualification for an exemption from backup withholding and
the procedure for obtaining such exemption.
 
     If backup withholding applies, the Depositary is required to withhold 31%
of any payments made to the shareholder. Backup withholding is not an additional
tax. Rather, the tax liability of persons subject to backup withholding will be
reduced by the amount of tax withheld. If withholding results in an overpayment
of taxes, a refund may be obtained from the Internal Revenue Service.
 
PURPOSE OF SUBSTITUTE FORM W-9
 
     To prevent backup withholding on payments that are made to a shareholder
with respect to Common Shares purchased pursuant to the Offer, the shareholder
is required to notify the Depositary of such shareholder's correct TIN by
completing the form below certifying (a) that the TIN provided on Substitute
Form W-9 is correct (or that such shareholder is awaiting a TIN), and (b) that
(i) such shareholder has not been notified by the Internal Revenue Service that
such shareholder is subject to backup withholding as a result of a failure to
report all interest or dividends or (ii) the Internal Revenue Service has
notified such shareholder that such shareholder is no longer subject to backup
withholding.
 
WHAT NUMBER TO GIVE THE DEPOSITARY
 
     The shareholder is required to give the Depositary the social security
number or employer identification number of the record holder of the Common
Shares tendered hereby. If the Common Shares are in more than one name or are
not in the name of the actual owner, consult the enclosed Guidelines for
Certification of Taxpayer Identification Number on Substitute Form W-9 for
additional guidance on which number to report. If the tendering shareholder has
not been issued a TIN and has applied for a number or intends to apply for a
number in the near future, the shareholder should write "Applied For" in the
space provided for the TIN in Part 1, and sign and date the Substitute Form W-9.
If "Applied For" is written in Part 1 and the Depositary is not provided with a
TIN within 60 days, the Depositary will withhold 31% of all payments of the
purchase price to such shareholder until a TIN is provided to the Depositary.
 
                                       10
<PAGE>   12
 
            ALL TENDERING STOCKHOLDERS MUST COMPLETE THE FOLLOWING:
             PAYER'S NAME: CHASEMELLON SHAREHOLDER SERVICES, L.L.C.
- --------------------------------------------------------------------------------
 
<TABLE>
<S>                             <C>                                               <C>
SUBSTITUTE                       PART 1 -- Taxpayer Identification Number -- For      -------------------------------
 FORM W-9                        all accounts, enter your taxpayer                        Social Security Number
 DEPARTMENT OF THE               identification number in the box at right. (For                    OR
 TREASURY                        most individuals, this is your social security
 INTERNAL REVENUE SERVICE        number. If you do not have a number, see             -------------------------------
                                 Obtaining a Number in the enclosed Guidelines        Employer Identification Number
 PAYER'S REQUEST FOR TAXPAYER    for Certification of Taxpayer Identification      (If awaiting TIN write "Applied For")
 IDENTIFICATION NUMBER ("TIN")   Number of Substitute Form W-9.) Certify by
                                 signing and dating below. Note: If the account
                                 is in more than one name, see the chart in the
                                 enclosed Guidelines to determine which number
                                 to give the payer.
                                ----------------------------------------------------------------------------------------
                                 PART 2 -- For Payees Exempt From Backup Withholding, see the enclosed Guidelines and
                                 complete as instructed therein.
- -------------------------------------------------------------------------------------------------------------------------
CERTIFICATION -- Under penalties of perjury, I certify that:
(1) The number shown on this form is my correct Taxpayer Identification Number (or I am waiting for a number to be issued
to me), and
(2) I am not subject to backup withholding because I have not been notified by the Internal Revenue Service (the "IRS")
    that I am subject to backup withholding as a result of failure to report all interest or dividends, or the IRS has
    notified me that I am no longer subject to backup withholding.
CERTIFICATE INSTRUCTIONS -- You must cross out item (2) above if you have been notified by the IRS that you are subject
to backup withholding because of underreporting interest or dividends on your tax return. However, if after being
notified by the IRS that you were subject to backup withholding, you received another notification from the IRS that you
are no longer subject to backup withholding, do not cross out item (2). (Also see instructions in the enclosed
Guidelines.)
- -------------------------------------------------------------------------------------------------------------------------
 Signature  Date  __________  , 1998
- -------------------------------------------------------------------------------------------------------------------------
</TABLE>
 
NOTE: FAILURE TO COMPLETE AND RETURN THIS FORM MAY RESULT IN BACKUP WITHHOLDING
      OF 31% OF ANY PAYMENTS MADE TO YOU PURSUANT TO THE OFFER. PLEASE REVIEW
      THE ENCLOSED GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
      NUMBER ON SUBSTITUTE FORM W-9 FOR ADDITIONAL DETAILS.
 
      YOU MUST COMPLETE THE FOLLOWING CERTIFICATE IF YOU WRITE "APPLIED FOR" IN
      THE SPACE PROVIDED FOR THE TIN IN PART 1 OF SUBSTITUTE FORM W-9
 
- --------------------------------------------------------------------------------
 
             CERTIFICATE OF AWAITING TAXPAYER IDENTIFICATION NUMBER
 
      I certify under penalties of perjury that a taxpayer identification
 number has not been issued to me, and either (1) I have mailed or delivered an
 application to receive a taxpayer identification number to the appropriate
 Internal Revenue Service Center or Social Security Administration Office or
 (2) I intend to mail or deliver an application in the near future. I
 understand that if I do not provide a taxpayer identification number by the
 time of payment, 31% of all reportable payments made to me will be withheld.
 
 ==============================================================
               Signature                                  Date
 
 -------------------------------------------------------------
          Name (Please Print)
- --------------------------------------------------------------------------------
<PAGE>   13
 
     Any questions or requests for assistance may be directed to the Information
Agent or the Dealer Manager at their respective telephone numbers and locations
listed below. Additional copies of the Offer to Purchase, the Supplement, the
revised Letter of Transmittal and the Notice of Guaranteed Delivery may be
obtained from the Information Agent at its address and telephone numbers set
forth below. Holders of Common Shares may also contact their broker, dealer,
commercial bank or trust company or other nominee for assistance concerning the
Offer.
 
                    The Information Agent for the Offer is:
 
                        [GEORGESON & COMPANY INC. LOGO]
 
                               Wall Street Plaza
                               New York, NY 10005
                Bankers and Brokers call collect: (212) 440-9800
                   All Others Call Toll-Free: (800) 223-2064
               INTERNET: World Wide Web http://www.georgeson.com
 
                      The Dealer Manager for the Offer is:
 
                     CREDIT SUISSE FIRST BOSTON CORPORATION
 
                             Eleven Madison Avenue
                               New York, NY 10010
                         Call Toll Free: (800) 863-6558
 
June 10, 1998

<PAGE>   1
 
                                                                Exhibit (a)(30)
 
                         NOTICE OF GUARANTEED DELIVERY
                                      FOR
 
                        TENDER OF SHARES OF COMMON STOCK
                                       OF
 
                               ALLIED GROUP, INC.
                   (NOT TO BE USED FOR SIGNATURE GUARANTEES)
 
     This revised Notice of Guaranteed Delivery, or one substantially in the
form hereof, must be used to accept the Offer (as defined below) (i) if
certificates ("Common Share Certificates") evidencing shares of common stock, no
par value (the "Common Shares"), of Allied Group, Inc., an Iowa corporation (the
"Company"), are not immediately available, (ii) if Common Share Certificates and
all other required documents cannot be delivered to ChaseMellon Shareholder
Services, L.L.C., as Depositary (the "Depositary"), prior to the Expiration Date
(as defined in Section 1 of the Supplement (as defined below)) or (iii) if the
procedure for delivery by book-entry transfer cannot be completed on a timely
basis. This revised Notice of Guaranteed Delivery may be delivered by hand or
mail or transmitted by telegram or facsimile transmission to the Depositary and
must include a guarantee by an Eligible Institution (as defined in the Offer to
Purchase (as defined below)) and a representation that the shareholder owns the
Common Shares, and that the tender of the Common Shares effected thereby
complies with Rule 14e-4 under the Securities Exchange Act of 1934, as amended,
each in the form set forth in this Notice of Guaranteed Delivery. See "Section
3. Procedures for Tendering Common Shares" of the Offer to Purchase as
supplemented by Section 2 of the Supplement.
 
                        The Depositary for the Offer is:
 
                    ChaseMellon Shareholder Services, L.L.C.
 
<TABLE>
<S>                                    <C>                             <C>
              By Mail:                 By Overnight Courier Delivery:                By Hand:
        Post Office Box 3301             85 Challenger Road -- Mail          120 Broadway, 13th Floor
     South Hackensack, NJ 07606                 Drop - Reorg                    New York, NY 10271
        Attn: Reorganization             Ridgefield Park, NJ 07660             Attn: Reorganization
             Department                     Attn: Reorganization                    Department
                                                 Department
</TABLE>
 
                           By Facsimile Transmission:
                                 (201) 329-8936
                             Confirm by Telephone:
                                 (201) 296-4860
 
     DELIVERY OF THIS REVISED NOTICE OF GUARANTEED DELIVERY TO AN ADDRESS OTHER
THAN AS SET FORTH ABOVE, OR TRANSMISSION OF INSTRUCTIONS VIA FACSIMILE
TRANSMISSION OTHER THAN AS SET FORTH ABOVE, WILL NOT CONSTITUTE A VALID
DELIVERY.
 
     This revised Notice of Guaranteed Delivery is not to be used to guarantee
signatures. If a signature on a revised Letter of Transmittal is required to be
guaranteed by an "Eligible Institution" under the instructions thereto, such
signature guarantee must appear in the applicable space provided in the
signature box on the revised Letter of Transmittal.
 
                THE GUARANTEE INCLUDED HEREIN MUST BE COMPLETED.
<PAGE>   2
 
Ladies and Gentlemen:
 
     The undersigned hereby tenders to Nationwide Group Acquisition Corporation,
an Ohio corporation and a wholly owned subsidiary of Nationwide Mutual Insurance
Company, an Ohio mutual insurance company, upon the terms and subject to the
conditions set forth in the Offer to Purchase dated May 19, 1998 (the "Offer to
Purchase"), the Supplement thereto dated June 10, 1998 (the "Supplement") and
the revised Letter of Transmittal (which, as amended from time to time, together
constitute the "Offer"), receipt of each of which is hereby acknowledged, the
number of Common Shares specified below pursuant to the guaranteed delivery
procedure described in "Section 3. Procedures for Tendering Common Shares" of
the Offer to Purchase as supplemented by Section 2 of the Supplement.
 
Number of Common Shares:
 
Common Share Certificate Nos.
(If Available):
 
- ---------------------------------------------------
 
- ---------------------------------------------------
 
    [ ]Check box if Common Shares will be
        delivered by book-entry transfer
 
Account No.
- -----------------------------------
- ---------------------------------------------------
 
- ---------------------------------------------------
SIGNATURE(S) OF HOLDER(S)
 
Dated:  ________ , 1998
 
Name(s) of Holders:
 
- ---------------------------------------------------
 
- ---------------------------------------------------
Please Type or Print
 
- ---------------------------------------------------
Address
 
- ---------------------------------------------------
Zip Code
 
- ---------------------------------------------------
Area Code and Telephone No.
<PAGE>   3
 
                THE GUARANTEE SET FORTH BELOW MUST BE COMPLETED
 
                                   GUARANTEE
 
                   (NOT TO BE USED FOR SIGNATURE GUARANTEES)
 
     The undersigned, a firm that is a commercial bank, broker, dealer, credit
union, savings association or other entity which is a member in good standing of
the Securities Transfer Agents Medallion Program, the New York Stock Exchange
Medallion Signature Guarantee Program or the Stock Exchange Medallion Program
(each, an "Eligible Institution") hereby (a) represents that the above named
person(s) "own(s)" the Common Shares tendered hereby within the meaning of Rule
14e-4 under the Securities Exchange Act of 1934, as amended ("Rule 14e-4"), (b)
represents that the tender of Common Shares effected hereby complies with Rule
14e-4, and (c) guarantees delivery to the Depositary, at one of its addresses
set forth above, of Common Share Certificates tendered hereby in proper form for
transfer, or confirmation of book-entry transfer of such Common Shares into the
account maintained by the Depositary at The Depository Trust Company or
Philadelphia Depository Trust Company, in each case with delivery of a properly
completed and duly executed revised Letter of Transmittal (or a facsimile
thereof) with any required signature guarantees, or an Agent's Message (as
defined in "Section 3. Procedures for Tendering Common Shares" of the Offer to
Purchase), and any other documents required by the revised Letter of
Transmittal, within three (3) New York Stock Exchange, Inc. trading days after
the date of execution of this revised Notice of Guaranteed Delivery.
 
     The Eligible Institution that completes this form must communicate the
guarantee to the Depositary and must deliver the revised Letter of Transmittal
and the Common Share Certificates to the Depositary within the time period shown
herein. Failure to do so could result in financial loss to such Eligible
Institution. All terms used herein have the meanings set forth in the Offer to
Purchase as supplemented by the Supplement.
 
                                 (PLEASE PRINT)
 
Name:
- --------------------------------------------------------------------------------
 
Address:
- --------------------------------------------------------------------------------
                                                                      (Zip Code)
 
AUTHORIZED SIGNATURE:
- --------------------------------------------------------------------------------
 
Name:
- --------------------------------------------------------------------------------
 
- --------------------------------------------------------------------------------
 
Title:
- --------------------------------------------------------------------------------
 
Daytime Area Code and Tel. No.:
- --------------------------------------------------------------------------
 
Dated:
- --------------------------------------------------------------------------------
 
NOTE: DO NOT SEND COMMON SHARE CERTIFICATES WITH THIS REVISED NOTICE OF
      GUARANTEED DELIVERY. COMMON SHARE CERTIFICATES SHOULD BE SENT WITH YOUR
      REVISED LETTER OF TRANSMITTAL.

<PAGE>   1
 
                                                                 Exhibit (a)(31)
 
[CREDIT SUISSE/FIRST BOSTON LOGO]
                                     CREDIT SUISSE FIRST BOSTON CORPORATION
 
                               Eleven Madison Avenue    Telephone (212) 325-2000
                           New York, NY 10010-3829
                               SUPPLEMENT TO THE
                           OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
 
                                       OF
 
                               ALLIED GROUP, INC.
                                       AT
 
                              $48.25 NET PER SHARE
 
                                       BY
 
                    NATIONWIDE GROUP ACQUISITION CORPORATION
                          A WHOLLY OWNED SUBSIDIARY OF
 
                      NATIONWIDE MUTUAL INSURANCE COMPANY
 
      THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M., NEW YORK
      CITY TIME, ON MONDAY, AUGUST 31, 1998, UNLESS THE OFFER IS EXTENDED.
 
                                                                   June 10, 1998
 
To Brokers, Dealers, Commercial Banks,
  Trust Companies and Other Nominees:
 
     We have been appointed by Nationwide Group Acquisition Corporation
("Purchaser"), an Ohio corporation and a wholly owned subsidiary of Nationwide
Mutual Insurance Company, an Ohio mutual insurance company ("Parent"), to act as
Dealer Manager in connection with Purchaser's offer to purchase all outstanding
shares of common stock, no par value (the "Common Shares"), of Allied Group
Inc., an Iowa corporation (the "Company"), at a price of $48.25 per Common
Share, net to the seller in cash, without interest thereon, upon the terms and
subject to the conditions set forth in Purchaser's Offer to Purchase dated May
19, 1998 (the "Offer to Purchase"), the Supplement thereto dated June 10, 1998
(the "Supplement") and the revised Letter of Transmittal (which, as amended from
time to time, together constitute the "Offer") enclosed herewith. Please furnish
copies of the enclosed materials to those of your clients for whose accounts you
hold Common Shares registered in your name or in the name of your nominee.
 
     THE OFFER IS CONDITIONED UPON, AMONG OTHER THINGS, (1) THERE BEING VALIDLY
TENDERED AND NOT PROPERLY WITHDRAWN PRIOR TO THE EXPIRATION OF THE OFFER THAT
NUMBER OF COMMON SHARES WHICH REPRESENT A MAJORITY OF THE COMMON SHARES OF THE
COMPANY OUTSTANDING ON A FULLY DILUTED BASIS (THE "MINIMUM CONDITION"); AND (2)
PARENT AND PURCHASER HAVING OBTAINED ALL INSURANCE REGULATORY APPROVALS
NECESSARY FOR THEIR ACQUISITION OF CONTROL OF THE COMPANY AND ITS INSURANCE
SUBSIDIARIES ON TERMS AND CONDITIONS SATISFACTORY TO PURCHASER AND SUCH
REGULATORY APPROVAL HAVING BECOME FINAL AND NON-APPEALABLE (THE "INSURANCE
REGULATORY APPROVAL CONDITION"). THE OFFER IS ALSO SUBJECT TO CERTAIN OTHER
TERMS AND CONDITIONS SET FORTH IN THE OFFER TO PURCHASE AS SUPPLEMENTED BY THE
SUPPLEMENT, HOWEVER, THE OFFER IS NOT CONDITIONED UPON PURCHASER OBTAINING
FINANCING.
<PAGE>   2
 
     For your information and for forwarding to your clients for whom you hold
Common Shares registered in your name or in the name of your nominee, or who
hold Common Shares registered in their own names, we are enclosing the following
documents:
 
          1. The Supplement dated June 10, 1998;
 
          2. The revised Letter of Transmittal for your use and for the
     information of your clients. Facsimile copies of the revised Letter of
     Transmittal may be used to tender Common Shares;
 
          3. The revised Notice of Guaranteed Delivery to be used to accept the
     Offer if a shareholder's certificates evidencing such shareholder's Common
     Shares and all other required documents are not immediately available or
     cannot be delivered to ChaseMellon Shareholder Services, L.L.C. (the
     "Depositary") by the Expiration Date (as defined in Section 1 of the
     Supplement) or if the procedure for book-entry transfer cannot be completed
     on a timely basis;
 
          4. A printed form of a letter which may be sent to your clients for
     whose accounts you hold Common Shares registered in your name or in the
     name of your nominee, with space provided for obtaining such clients'
     instructions with regard to the Offer; and
 
          5. The guidelines for Certification of Taxpayer Identification Number
     on Substitute Form W-9.
 
     YOUR PROMPT ACTION IS REQUESTED. WE URGE YOU TO CONTACT YOUR CLIENTS AS
PROMPTLY AS POSSIBLE. PLEASE NOTE THAT THE OFFER AND WITHDRAWAL RIGHTS EXPIRE AT
5:00 P.M., NEW YORK CITY TIME, ON MONDAY, AUGUST 31, 1998, UNLESS THE OFFER IS
EXTENDED.
 
     Your attention is invited to the following:
 
          1. The tender price is $48.25 per Common Share, net to the seller in
     cash, without interest thereon, upon the terms and subject to the
     conditions set forth in the Offer.
 
          2. The Offer is being made for all outstanding Common Shares.
 
          3. The Offer and withdrawal rights will expire at 5:00 P.M. midnight,
     New York City time, on Monday, August 31, 1998, unless the Offer is
     extended.
 
          4. The Offer is conditioned upon, among other things, the Minimum
     Condition and the Insurance Regulatory Approval Condition. The Offer is
     also subject to certain other terms and conditions set forth in the Offer
     to Purchase as supplemented by the Supplement, however, the Offer is not
     conditioned upon Purchaser obtaining financing.
 
          5. Except as otherwise provided in Instruction 6 of the revised Letter
     of Transmittal, tendering shareholders will not be obligated to pay stock
     transfer taxes with respect to the purchase of Common Shares by Purchaser
     pursuant to the Offer. However, backup federal income tax withholding at a
     rate of 31% may be required, unless an exemption applies or unless the
     required taxpayer identification information is provided. See Instruction
     10 of, and "Important Tax Information" in, the revised Letter of
     Transmittal.
 
          6. In all cases, payment for Common Shares accepted for payment
     pursuant to the Offer will be made only after timely receipt by the
     Depositary of certificates evidencing such Common Shares (or a confirmation
     of a book-entry transfer of such Common Shares into the Depositary's
     account at the Book-Entry Transfer Facility (as defined in the Offer to
     Purchase)), a Letter of Transmittal or revised Letter of Transmittal (or
     facsimile thereof) properly completed and duly executed, with any required
     signature guarantees, or, in the case of a book-entry transfer, an Agent's
     Message (as defined in the Offer to Purchase), and any other documents
     required by the Letter of Transmittal or revised Letter of Transmittal. See
     "Procedures for Tendering Common Shares" of the Offer to Purchase as
     supplemented by Section 2 of the Supplement.
<PAGE>   3
 
     If holders of Common Shares wish to tender, but it is impracticable for
them to forward their certificates evidencing such Common Shares or other
required documents prior to the Expiration Date or, if applicable, to comply
with the book-entry transfer procedures on a timely basis, a tender may be
effected by following the guaranteed delivery procedure described in "Procedures
for Tendering Common Shares" of the Offer to Purchase as supplemented by Section
2 of the Supplement.
 
     Purchaser will not pay any fees or commissions to any broker, dealer or
other person (other than the Dealer Manager, the Depositary and the Information
Agent as described in the Offer to Purchase as supplemented by the Supplement)
in connection with the solicitation of tenders of Common Shares pursuant to the
Offer. However, Purchaser will reimburse you for customary mailing and handling
expenses incurred by you in forwarding any of the enclosed materials to your
clients. Purchaser will pay or cause to be paid any stock transfer taxes payable
with respect to the transfer of Common Shares to it, except as otherwise
provided in Instruction 6 of the revised Letter of Transmittal.
 
     Any inquiries you may have with respect to the Offer should be addressed to
Credit Suisse First Boston Corporation, the Dealer Manager, or Georgeson &
Company Inc., the Information Agent, at their respective addresses and telephone
numbers set forth on the back cover page of the Offer to Purchase and the
Supplement.
 
     Additional copies of the enclosed material may be obtained from the
Information Agent or the Dealer Manager at their respective addresses and
telephone numbers set forth on the back cover page of the Offer to Purchase and
the Supplement.
 
                                            Very truly yours,
 
                                            Credit Suisse First Boston
                                            Corporation
 
     NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU
OR ANY OTHER PERSON THE AGENT OF THE PARENT, THE PURCHASER, THE COMPANY, THE
DEALER MANAGER, THE INFORMATION AGENT OR THE DEPOSITARY, OR OF ANY AFFILIATE OF
ANY OF THEM, OR AUTHORIZE YOU OR ANY OTHER PERSON TO USE ANY DOCUMENT OR TO MAKE
ANY STATEMENT ON BEHALF OF ANY OF THEM IN CONNECTION WITH THE OFFER OTHER THAN
THE ENCLOSED DOCUMENTS AND THE STATEMENTS CONTAINED THEREIN.

<PAGE>   1
 
                                                                 Exhibit (a)(32)
 
                               SUPPLEMENT TO THE
 
                           OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
 
                                       OF
 
                               ALLIED GROUP, INC.
                                       AT
 
                          $48.25 NET PER COMMON SHARE
 
                                       BY
 
                    NATIONWIDE GROUP ACQUISITION CORPORATION
                          A WHOLLY OWNED SUBSIDIARY OF
 
                      NATIONWIDE MUTUAL INSURANCE COMPANY
           THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 5:00 P.M.,
 NEW YORK CITY TIME, ON MONDAY, AUGUST 31, 1998, UNLESS THE OFFER IS EXTENDED.
 
To Our Clients:
 
     Enclosed for your consideration is a Supplement dated June 10, 1998 (the
"Supplement") to the Offer to Purchase dated May 19, 1998 (the "Offer to
Purchase") and a revised Letter of Transmittal in connection with the offer by
Nationwide Group Acquisition Corporation ("Purchaser"), an Ohio corporation and
a wholly owned subsidiary of Nationwide Mutual Insurance Company, an Ohio mutual
insurance company ("Parent"), to purchase all outstanding shares of common
stock, no par value (the "Common Shares"), of Allied Group Inc., an Iowa
corporation (the "Company"), at a price of $48.25 per Common Share, net to the
seller in cash, without interest thereon, upon the terms and subject to the
conditions set forth in the Offer to Purchase, the Supplement, and the revised
Letter of Transmittal (which, as amended from time to time, together constitute
the "Offer").
 
     Shareholders who desire to tender Common Shares pursuant to the Offer and
whose certificates evidencing such Common Shares are not immediately available
or the procedures for book-entry transfer set forth in the Offer to Purchase as
supplemented by the Supplement cannot be completed on a timely basis or time
will not permit all required documents to reach ChaseMellon Shareholder
Services, L.L.C. (the "Depositary") prior to the Expiration Date (as defined in
the Supplement) may nevertheless tender their Common Shares according to the
guaranteed delivery procedures set forth in "Section 3. Procedures for Tendering
Common Shares" of the Offer to Purchase as supplemented by Section 2 of the
Supplement.
 
     We are (or our nominee is) the holder of record of Common Shares held by us
for your account. A TENDER OF SUCH COMMON SHARES CAN BE MADE ONLY BY US AS THE
HOLDER OF RECORD AND PURSUANT TO YOUR INSTRUCTIONS. THE REVISED LETTER OF
TRANSMITTAL IS FURNISHED TO YOU FOR YOUR INFORMATION ONLY AND CANNOT BE USED BY
YOU TO TENDER COMMON SHARES HELD BY US FOR YOUR ACCOUNT.
 
     We request instructions as to whether you wish to have us tender on your
behalf any or all of the Common Shares held by us for your account, upon the
terms and subject to the conditions set forth in the Offer.
<PAGE>   2
 
     Your attention is invited to the following:
 
          1. The tender price is $48.25 per Common Share, net to the seller in
     cash, without interest thereon, upon the terms and subject to the
     conditions set forth in the Offer.
 
          2. The Offer is being made for all outstanding Common Shares.
 
          3. The Offer and withdrawal rights will expire at 5:00 p.m., New York
     City time, on Monday, August 31, 1998, unless the Offer is extended.
 
          4. The Offer is conditioned upon, among other things, (1) there being
     validly tendered and not properly withdrawn prior to the expiration of the
     Offer the number of Common Shares which represent a majority of the Common
     Shares of the Company outstanding on a fully diluted basis, and (2) Parent
     and Purchaser having obtained all insurance regulatory approvals necessary
     for their acquisition of control of the Company and its insurance
     subsidiaries on terms and conditions satisfactory to Purchaser and such
     regulatory approval having become final and non-appealable. The Offer is
     also subject to certain other terms and conditions set forth in the Offer
     to Purchase as supplemented by the Supplement, however, the Offer is not
     conditioned upon Purchaser obtaining financing.
 
          5. Except as otherwise provided in Instruction 6 of the revised Letter
     of Transmittal, tendering shareholders will not be obligated to pay stock
     transfer taxes with respect to the purchase of Common Shares by Purchaser
     pursuant to the Offer. However, backup federal income tax withholding at a
     rate of 31% may be required, unless an exemption applies or unless the
     required taxpayer identification information is provided. See Instruction
     10 of, and "Important Tax Information" in, the revised Letter of
     Transmittal.
 
          6. In all cases, payment for Common Shares purchased pursuant to the
     Offer will be made only after timely receipt by the Depositary of
     certificates evidencing, or a Book-Entry Confirmation (as defined in the
     Offer to Purchase) with respect to, such Common Shares and a Letter of
     Transmittal or revised Letter of Transmittal (or facsimile thereof),
     properly completed and duly executed, with all required signature
     guarantees, or, in the case of a book-entry transfer, an Agent's Message
     (as defined in the Offer to Purchase), and any other documents required by
     the Letter of Transmittal or revised Letter of Transmittal. See "Section 3.
     Procedures for Tendering Common Shares" of the Offer to Purchase as
     supplemented by Section 2 of the Supplement.
 
     If you wish to have us tender any or all of your Common Shares, please so
instruct us by completing, executing and returning to us the form contained in
this letter. An envelope in which to return your instructions to us is enclosed.
If you authorize the tender of your Common Shares, all such Common Shares will
be tendered unless otherwise specified in your instructions. Your instructions
should be forwarded to us in ample time to permit us to submit a tender on your
behalf prior to the expiration of the Offer.
 
     THE OFFER IS MADE SOLELY BY THE OFFER TO PURCHASE, THE SUPPLEMENT AND THE
REVISED LETTER OF TRANSMITTAL, AS AMENDED FROM TIME TO TIME, AND IS BEING MADE
TO ALL HOLDERS OF COMMON SHARES.
 
     Purchaser is not aware of any jurisdiction where the making of the Offer is
prohibited by administrative or judicial action pursuant to any valid state
statute. If Purchaser becomes aware of any valid state statute prohibiting the
making of the Offer or the acceptance of Common Shares pursuant thereto,
Purchaser will make a good faith effort to comply with such state statute. If,
after such good faith effort, Purchaser cannot comply with such state statute,
the Offer will not be made to (nor will tenders be accepted from or on behalf
of) the holders of Common Shares in such state. In any jurisdiction where the
securities, blue sky or other laws require the Offer to be made by a licensed
broker or dealer, the Offer shall be deemed to be made on behalf of Purchaser by
Credit Suisse First Boston Corporation or one or more registered brokers or
dealers licensed under the laws of such jurisdiction.
<PAGE>   3
 
               INSTRUCTIONS WITH RESPECT TO THE SUPPLEMENT TO THE
                           OFFER TO PURCHASE FOR CASH
                   ALL OUTSTANDING SHARES OF COMMON STOCK OF
 
                               ALLIED GROUP, INC.
 
     The undersigned acknowledge(s) receipt of your letter, the enclosed
Supplement dated June 10, 1998 to the Offer to Purchase dated May 19, 1998 and
the revised Letter of Transmittal in connection with the offer by Nationwide
Group Acquisition Corporation, an Ohio corporation, and a wholly owned
subsidiary of Nationwide Mutual Insurance Company, an Ohio mutual insurance
company, to purchase all outstanding shares of common stock, no par value (the
"Common Shares"), of Allied Group, Inc., an Iowa corporation, at a price of
$48.25 per Common Share, net to the seller in cash, without interest thereon.
 
     This will instruct you to tender the number of Common Shares indicated
below (or, if no number is indicated below, all Common Shares) that are held by
you for the account of the undersigned, upon the terms and subject to the
conditions set forth in the Offer to Purchase as supplemented by the Supplement.
 
                            Number of Common Shares
                                to Be Tendered:
                           ____________ Common Shares*
 
Dated:                     , 1998
 
SIGN HERE
 
- ---------------------------------------------------
 
- ---------------------------------------------------
Signature(s)
 
- ---------------------------------------------------
 
- ---------------------------------------------------
Please type or print name(s)
 
- ---------------------------------------------------
 
- ---------------------------------------------------
Please type or print address
 
- ---------------------------------------------------
Area Code and Telephone Number
 
- ---------------------------------------------------
Taxpayer Identification or
Social Security Number
 
- ------------
 
* Unless otherwise indicated, it will be assumed that all Common Shares held by
  us for your account are to be tendered.

<PAGE>   1


                                                             Exhibit (c)(1)

                              SHAREHOLDER AGREEMENT

                  SHAREHOLDER AGREEMENT, dated as of June 3, 1998, between
Nationwide Mutual Insurance Company, an Ohio mutual insurance company
("Nationwide"), and Allied Mutual Insurance Company, an Iowa mutual insurance
company (the "Securityholder").

                  WHEREAS, Nationwide, Nationwide Group Acquisition Corporation,
an Ohio corporation and wholly-owned subsidiary of Nationwide ("Sub"), and
Allied Group, Inc., an Iowa corporation (the "Company"), propose to enter into
an Agreement and Plan of Merger, dated the date hereof (as the same may be
amended or supplemented, the "Merger Agreement"), which provides for a cash
tender offer by Sub (as such tender offer may hereafter be amended from time to
time, the "Offer") to purchase all shares of common stock, no par value, of the
Company (the "Common Shares") and, following the consummation of the Offer, the
merger of Sub with the Company (the "Merger");

                  WHEREAS, the Securityholder is the record and beneficial owner
of the number of (i) Common Shares, and (ii) shares of 6 3/4% Series Preferred
Stock, no par value, of the Company and (collectively, the "Preferred Shares")
set forth on Schedule A hereto; such securities, as they may be adjusted by
stock dividend, stock split, recapitalization, combination or exchange of
shares, merger, consolidation, reorganization or other change or transaction of
or by the Company, together with securities that may be acquired after the date
hereof by the Securityholder, including Common Shares issuable upon the exercise
of options to purchase Common Shares (as the same may be adjusted as aforesaid),
being collectively referred to herein as the "Securities"; and

                  WHEREAS, as a condition to their willingness to enter into the
Merger Agreement, Nationwide has requested that the Securityholder enter into
this Agreement (capitalized terms not otherwise defined herein shall have the
meanings set forth in the Merger Agreement);

                  NOW, THEREFORE, to induce Nationwide to enter into, and in
consideration of it entering into, the Merger Agreement, and in consideration of
the premises and the representations, warranties and agreements contained
herein, the parties hereto, intending to be legally bound hereby, agree as
follows:

                                        1
<PAGE>   2
                  1. Tender of Common Shares. The Securityholder agrees to
tender (or cause the record owner thereof to tender), pursuant to and in
accordance with the terms of the Offer, and not to withdraw, all Securities
which are Common Shares. Stockholder hereby acknowledges and agrees that
Nationwide's and Sub's obligation to accept for payment and pay for Common
Shares in the Offer, including any Securities tendered by Securityholder, is
subject to the terms and conditions of the Offer. The parties agree that the
Securityholder will, for all Common Shares tendered by Securityholder in the
Offer and accepted for payment and paid for by Sub, receive the same per share
consideration paid to other shareholders who have tendered into the Offer.

                  2. Covenants of the Securityholder. The Securityholder agrees
as follows:

                  (a) The Securityholder shall not, except as contemplated by
the terms of this Agreement, (i) sell, transfer, pledge, assign or otherwise
dispose of, or enter into any Contract (as defined below), option or other
arrangement (including any profit sharing arrangement) or understanding with
respect to the sale, transfer, pledge, assignment or other disposition of, the
Securities to any person other than Nationwide or Nationwide's designee, or (ii)
enter into any voting arrangement, whether by proxy, voting agreement, voting
trust, power-of-attorney or otherwise, with respect to the Securities.

                  (b) The Securityholder shall not, nor shall the Securityholder
permit any investment banker, financial adviser, attorney, accountant or other
representative or agent of the Securityholder to, directly or indirectly (i)
solicit, initiate or knowingly encourage (including by way of furnishing
information), or knowingly facilitate any inquiries or the making of any
proposal which constitutes, or may reasonably be expected to lead to, any
Acquisition Proposal or (ii) participate in any discussions or negotiations
regarding any Acquisition Proposal.

                  (c) At any meeting of shareholders of the Company called to
vote upon the Merger and the Merger Agreement or at any adjournment thereof or
in any other circumstances upon which a vote, consent or other approval
(including by written consent) with respect to the Merger and the Merger
Agreement is sought, the Securityholder shall, including by initiating a written
consent solicitation if requested by Nationwide, vote (or cause to be voted)
such Securityholder's Securities in favor of the Merger, the adoption of the
Merger Agreement and the approval of the other transactions contemplated by the
Merger Agreement. At any meeting of sharehold-

                                       2
<PAGE>   3
ers of the Company or at any adjournment thereof or in any other circumstances
upon which the Securityholder's vote, consent or other approval is sought, the
Securityholder shall vote (or cause to be voted) the Securityholder's Securities
against (i) any merger (other than the Merger), consolidation, combination, sale
of substantial assets, reorganization, recapitalization, dissolution,
liquidation or winding up of or by the Company or any other Acquisition Proposal
(collectively, "Alternative Transactions") or (ii) any amendment of the
Company's Certificate of Incorporation or by-laws or other proposal or
transaction involving the Company or any of its subsidiaries, which amendment or
other proposal or transaction would in any manner impede, frustrate, prevent or
nullify, the Merger, the Merger Agreement or any of the other transactions
contemplated by the Merger Agreement including any consent to the treatment of
any Securities in or in connection with such transaction (collectively,
"Frustrating Transactions").

                  3. Grant of Irrevocable Proxy Coupled with an Interest;
Appointment of Proxy.

                  (a) Subject to governmental approvals, the Securityholder
hereby irrevocably grants to, and appoints, any individual who shall be
designated by Nationwide as the Securityholder's proxy and attorney-in-fact
(with full power of substitution), for and in the name, place and stead of the
Securityholder, to vote the Securityholder's Securities, or grant a consent or
approval in respect of such Securities, at any meeting of shareholders of the
Company or at any adjournment thereof or in any other circumstances upon which
their vote, consent or other approval is sought, (i) in favor of the Merger, the
adoption by the Company of the Merger Agreement and the approval of the other
transactions contemplated by the Merger Agreement, and (ii) against any
Alternative Transaction or Frustrating Transaction.

                  (b) The Securityholder represents that any proxies heretofore
given in respect of the Securityholder's Securities are not irrevocable, and
that any such proxies are hereby revoked.

                  (c) THE SECURITYHOLDER HEREBY AFFIRMS THAT THE PROXY SET FORTH
IN THIS SECTION 3 IS COUPLED WITH AN INTEREST AND IS IRREVOCABLE UNTIL SUCH TIME
AS THIS AGREEMENT TERMINATES IN ACCORDANCE WITH ITS TERMS. The Securityholder
hereby further affirms that the irrevocable proxy is given in connection with
the execution of the Merger Agreement, and that such irrevocable proxy is given
to secure the performance of the duties of the Securityholder under this
Agreement.

                                       3
<PAGE>   4
The Securityholder hereby ratifies and confirms all that such irrevocable proxy
may lawfully do or cause to be done by virtue hereof.

                  4. Acquisition Proposals.

                  (a) Notwithstanding anything to the contrary contained in this
Agreement, during any period of time that the Company is not prohibited by the
Merger Agreement from (A) providing information in response to a request
therefor by a Person who has made an unsolicited bona fide written Acquisition
Proposal; (B) engaging in any negotiations or discussions with any Person who
has made an unsolicited bona fide written Acquisition Proposal; or (C)
recommending an Acquisition Proposal to the shareholders of the Company, the
Securityholder's obligations under Sections 1, 2 and 3 of this Agreement shall
be deemed inoperative.

                  (b) Notwithstanding anything to the contrary contained in this
Agreement, during any period of time that the Securityholder is not prohibited
by the Agreement and Plan of Merger, dated as of the date hereof, by and between
Securityholder and Nationwide (the "Allied Mutual Merger Agreement") from (A)
providing information in response to a request therefor by a Person who has made
an unsolicited bona fide written Acquisition Proposal; (B) engaging in any
negotiations or discussions with any Person who has made an unsolicited bona
fide written Acquisition Proposal; or (C) recommending an Acquisition Proposal
to the policyholders of the Securityholder, the Securityholder's obligations
under Sections 1, 2 and 3 of this Agreement shall be deemed inoperative. For
purposes of this Section 4(b), "Acquisition Proposal" shall have the meaning
ascribed thereto in the Allied Mutual Merger Agreement.

                  5. Representations and Warranties of the Securityholder. The
Securityholder hereby represents and warrants to Nationwide as follows:

                  (a) Authority. The Securityholder has all requisite corporate
power and authority to execute and deliver this Agreement and to consummate the
transactions contemplated hereby. The execution, delivery and performance of
this Agreement and the consummation of the transactions contemplated hereby have
been duly authorized by the Securityholder. This Agreement has been duly
executed and delivered by the Securityholder and, assuming this Agreement
constitutes a valid and binding obligation of Nationwide, constitutes a valid
and binding obligation of the Securityholder enforceable against the
Securityholder in accordance with its terms, except that (i) such enforcement
may be subject to bankruptcy, insolvency, reorgani-

                                       4
<PAGE>   5
zation, moratorium or other similar laws now or hereafter in effect relating to
creditors' rights generally and (ii) the remedy of specific performance and
injunctive relief may be subject to equitable defenses and to the discretion of
the court before which any proceeding therefor may be brought. Except for the
informational filings with the Securities and Exchange Commission and except for
any state insurance department approvals or filings, neither the execution,
delivery or performance of this Agreement by the Securityholder nor the
consummation by the Securityholder of the transactions contemplated hereby will
(i) require any filing with, or permit, authorization, consent or approval
(collectively, "Governmental Approvals") of, any federal, state, local or
municipal foreign or other government or subdivision, branch, department or
agency thereof or any governmental or quasi-governmental authority of any
nature, including any court or other tribunal, (a "Governmental Entity"), except
where the failure to obtain any such Governmental Approvals would not be
reasonably likely to adversely affect the transactions contemplated hereby, (ii)
result in a violation or breach of, or constitute (with or without due notice or
lapse of time or both) a default under, or give rise to any right of
termination, amendment, cancellation or acceleration under, or result in the
creation of any lien upon any of the properties or assets of the Securityholder
under, any of the terms, conditions or provisions of any note, bond, mortgage,
indenture, lease, license, permit, concession, franchise, contract, agreement or
other instrument or obligation (a "Contract") to which the Securityholder is a
party or by which the Securityholder or any of the Securityholder's properties
or assets, including the Securityholder's Securities, may be bound, except for
such violations, breaches, defaults, rights of termination, amendment,
cancellation and acceleration and liens which would not be reasonably likely to
adversely affect the transactions contemplated hereby or (iii) violate any
judgment, order, writ, preliminary or permanent injunction or decree (an
"Order") or any statute, law, ordinance, rule or regulation of any Governmental
Entity (a "Law") applicable to the Securityholder or any of the Securityholder's
properties or assets, including the Securityholder's Securities, except for such
violations which would not be reasonably likely to adversely affect the
transactions contemplated hereby

                  (b) The Securities. The Securityholder's Securities and the
certificates representing such Securities are now, and at all times during the
term hereof will be, held by such Securityholder, or by a nominee or custodian
for the benefit of such Securityholder, and the Securityholder has good and
marketable title to such Securities, free and-clear of any liens, proxies,
voting trusts or agreements, understandings or arrangements, except for any such
liens or proxies arising hereunder and the agreements made hereby. The
Securityholder owns of record or beneficially no securities of the Company, or
any options, warrants or rights exercisable for

                                       5
<PAGE>   6
securities of the Company, other than such Securityholder's Securities, as set
forth on Schedule A hereto.

                  (c) Brokers. Except as provided in the Allied Mutual Merger
Agreement, no broker, investment banker, financial advisor or other person is
entitled to any broker's, finder's, financial advisor's or other similar fee or
commission in connection with the transactions contemplated by this Agreement
based upon arrangements made by or on behalf of the Securityholder.

                  (d) Merger Agreement. The Securityholder understands and
acknowledges that Nationwide is entering into the Merger Agreement in reliance
upon the Securityholder's execution and delivery of this Agreement.

                  6. Representations and Warranties of Nationwide. Nationwide
hereby represents and warrants to the Securityholder as follows:

                  (a) Authority. Nationwide has the requisite corporate power
and authority to execute and deliver this Agreement and to consummate the
transactions contemplated hereby. The execution, delivery and performance of
this Agreement by Nationwide and the consummation of the transactions
contemplated hereby have been duly authorized by all necessary corporate action
on the part of Nationwide. This Agreement has been duly executed and delivered
by Nationwide and, assuming this Agreement constitutes a valid and binding
obligation of the Securityholder, constitutes a valid and binding obligation of
Nationwide enforceable in accordance with its terms, except that (i) such
enforcement may be subject to bankruptcy, insolvency, reorganization, moratorium
or other similar laws now or hereafter in effect relating to creditors' rights
generally and (ii) the remedy of specific performance and injunctive relief may
be subject to equitable defenses and to the discretion of the court before which
any proceeding therefor may be brought.

                  (b) Securities Act. The Securities will be acquired in
compliance with, and Nationwide will not offer to sell or otherwise dispose of
any Securities so acquired by it in violation of any of, the Securities Exchange
Act of 1934, as amended, or the registration requirements of the Securities Act
of 1933, as amended.

                  7. Further Assurances. Except as otherwise provided in
Sections 4(a) and 4(b), the Securityholder will, from time to time, execute and
deliver, or cause to be executed and delivered, such additional or further
transfers, assignments, endorsements, consents and other instruments as
Nationwide may reasonably request

                                       6
<PAGE>   7
for the purpose of effectively carrying out the transactions contemplated by
this Agreement and to vest the power to vote the Securityholder's Securities as
contemplated by Section 3. Nationwide agrees to use its best efforts to take,
or cause to be taken, all actions necessary to comply promptly with all legal
requirements that may be imposed with respect to the transactions contemplated
by this Agreement.

                  8. Termination. This Agreement, and all rights and obligations
of the parties hereunder, shall terminate on the earlier of the termination of
the Merger Agreement in accordance with its terms and the termination of the
Allied Mutual Merger Agreement. Nothing in this Section 8 shall relieve any
party from liability for willful breach of this Agreement.

                  9. General Provisions.

                  (a) Assignment; Binding Effect. Neither this Agreement nor any
of the rights, interests or obligations hereunder shall be assigned by any of
the parties hereto (whether by operation of law or otherwise) without the prior
written consent of the other parties. Subject to the preceding sentence, this
Agreement shall be binding upon, inure to the benefit of, and be enforceable by,
the parties hereto and their respective successors and assigns.

                  (b) Amendments. This Agreement may not be amended except by an
instrument in writing signed by each of the parties hereto.

                  (c) Notice. All notices, consents, requests, approvals,
authorizations and other communications (collectively, "Notices") required or
permitted to be given hereunder by one party to another shall only be effective
if in writing. All Notices shall be sent (i) by registered or certified mail
(with return receipt requested), postage prepaid, or (ii) by Federal Express,
U.S. Post Office Express Mail, Airborne or similar overnight courier which
delivers, if requested, only upon signed receipt of the addressee (with such
signed receipt being requested), or (iii) by facsimile transmission, and
addressed or transmitted as follows or at such other address or facsimile
number, and to the attention of such other person, as the parties shall give
notice as herein provided:

                      If to Nationwide, to:

                      Nationwide Mutual Insurance Company
                      One Nationwide Plaza

                                       7
<PAGE>   8
                      Columbus, Ohio 43215
                      Attention:  David A. Diamond, Vice President -- Enterprise
                      Controller
                      Facsimile:  (614) 249-4462

                      with a copy to:

                      Nationwide Mutual Insurance Company
                      One Nationwide Plaza
                      Columbus, Ohio 43215
                      Attention:   Mark B. Koogler, Vice President and Associate
                                   General Counsel
                                   Roger A. Craig, Counsel
                      Facsimile:  (614) 249-7254

                      and

                      if to the Securityholder, to:

                      Allied Mutual Insurance Company
                      701 Fifth Avenue
                      Des Moines, Iowa  50391-2000
                      Attention:   John E. Evans, Chairman of the Board
                                   Douglas L. Andersen, President and Chief
                                   Executive Officer
                      Facsimile No.: 515-280-4399

                      with copies to:

                      Nyemaster, Goode, Voigts, West, Hansell & O'Brien
                      A Professional Corporation
                      700 Walnut Street, Suite 1600
                      Des Moines, Iowa  50309-3899
                      Attention: Mark C. Dickinson, Esq.
                      Facsimile No.: 515-283-3108

                      and

                                       8
<PAGE>   9
                      Skadden, Arps, Slate, Meagher & Flom LLP
                      919 Third Avenue
                      New York, New York  10022-3897
                      Attention: Jeffrey W. Tindell, Esq.
                      Facsimile No.: 212-451-7321

A Notice shall be effective upon receipt and shall be deemed to be received, if
sent by registered or certified mail, U.S. Post Office Express Mail, Federal
Express, Airborne or similar overnight courier, on the date of receipt by the
recipient as shown on the return receipt card, or if sent by facsimile, upon
receipt by the sender of an acknowledgment or transmission report generated by
the machine from which the facsimile was sent indicating that the facsimile was
sent in its entirety to the recipient's facsimile number; provided that if a
Notice is received by facsimile on a day which is not a Business Day, or after
5:00 p.m. on any Business Day at the addressee's location, such Notice shall be
deemed to be received by the recipient at 9:00 a.m. on the first Business Day
thereafter. Rejection or other refusal to accept or the inability to deliver
because of changed address of which no Notice was given shall be deemed to be
receipt of the Notice as of the date of such rejection, refusal or inability to
deliver.

                  (d) Interpretation. When a reference is made in this Agreement
to a Section, such reference shall be to a Section of this Agreement unless
otherwise indicated. The headings contained in this Agreement are for reference
purposes only and shall not affect in any way the meaning or interpretation of
this Agreement. Wherever the words "include", "includes" or "including" are used
in this Agreement, they shall be deemed to be followed by the words "without
limitation." The words "hereof", "herein" and "herewith" and words of similar
import shall, unless otherwise stated, be construed to refer to this Agreement
as a whole and not to any particular provision of this Agreement. The plural of
any defined term shall have a meaning correlative to such defined term, and
words denoting any gender shall include all genders. Where a word or phrase is
defined herein, each of its other grammatical forms shall have a corresponding
meaning. A reference to any party to this Agreement or any other agreement or
document shall include such party's successors and permitted assigns. A
reference to any legislation or to any provision of any legislation shall
include any modification or re-enactment thereof, any legislative provision
substituted therefor and all regulations and statutory instruments issued
thereunder or pursuant thereto. For purposes of this Agreement, "Person" shall
mean an individual, corporation, partnership, association, joint stock company,

                                       9
<PAGE>   10
limited liability company, Governmental Entity, trust, joint venture, labor
union, estate, unincorporated organization or other entity.

                  (e) Counterparts. This Agreement shall be executed in
duplicate and may be executed in counterparts each of which shall be deemed to
constitute an original and constitute one and the same instrument. Delivery of
an executed counterpart of a signature page to this Agreement by telecopier
shall be as effective as delivery of a manually executed counterpart of this
Agreement. In proving this Agreement, it shall not be necessary to produce or
account for more than one such counterpart signed by the party against whom
enforcement is sought.

                  (f) Entire Agreement. This Agreement (including the documents
and instruments referred to herein) constitutes the entire agreement and
supersedes all prior agreements and understandings, both written and oral, among
the parties with respect to the subject matter hereof.

                  (g) No Third-Party Beneficiaries. Notwithstanding anything
contained in this Agreement to the contrary, nothing in this Agreement,
expressed or implied, is intended to confer on any person other than the parties
hereto or their respective heirs, successors, executors, administrators and
assigns any rights, remedies, obligations or liabilities under or by reason of
this Agreement.

                  (h) Governing Law. This Agreement shall be governed and
construed in accordance with the laws of the State of Iowa without regard to any
conflicts or choice of law provisions thereof or of any other jurisdiction.

                  (i) Enforcement. The parties agree that irreparable damage
would occur in the event that any of the provisions of this Agreement were not
performed in accordance with their specific terms or were otherwise breached. It
is accordingly agreed that the parties shall be entitled to an injunction or
injunctions to prevent breaches of this Agreement and to enforce specifically
the terms and provisions of this Agreement in a court of the United States. This
being in addition to any other remedy to which they are entitled at law or in
equity. In addition, each of the parties hereto waives any right to trial by
jury with respect to any claim or proceeding related to or arising out of this
Agreement or any of the transactions contemplated hereby.

                                       10
<PAGE>   11
                  IN WITNESS WHEREOF, each of Nationwide and Securityholder has
caused this Agreement to be signed by its officer thereunto duly authorized, as
of the date first written above.


                                    NATIONWIDE MUTUAL INSURANCE
                                    COMPANY

                                    By: /s/ Mark B. Koogler
                                        ---------------------------------------
                                    Name:  Mark B. Koogler
                                    Title: Vice President and Associate General
                                           Counsel


                                    ALLIED MUTUAL INSURANCE
                                    COMPANY

                                    By: /s/ George T. Oleson
                                        ---------------------------------------
                                    Name:  George T. Oleson
                                    Title: Vice President and Corporate Counsel

                                       11
<PAGE>   12
<TABLE>
                                                   SCHEDULE A
<CAPTION>
                                             Common            Preferred
        Name and Address                     Shares              Shares            Warrants            Options
        ----------------                     ------              ------            --------            -------
<S>                                          <C>               <C>                                          
Allied Mutual Insurance Company              498,236           1,827,222              --                  --
</TABLE>

                                       12


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