Notwithstanding section 3 of chapter 32 of the General Laws, the state board of retirement shall grant William Pillsbury creditable service for the period of January 1990 to January 1999, inclusive, during which he served as a Director of the Office of Business and Industrial Development within the New Hampshire Department of Resources and Economic Development; provided, however, that he shall pay into the annuity savings fund, in one sum or in installments, as the board shall determine, an amount equal to the regular deductions which would have been deducted for said period together with regular deductions which would have would have been deducted for said period together with regular interest thereon.

   In the event that William Pillsbury shall retire before the completion of said payments, he shall, in addition to his actual membership service, be entitled to credit for the portion of the creditable service which the total of his actual payments, together with regular interest thereon to the date such retirement becomes effective, bears to the total amount of what his payment, together with regular interest thereon, would have been had he made a payment in one sum on the effective date of his retirement.