Any person who on July 1, 1998, was a member of the Employees' Retirement System of Georgia and was employed in a position otherwise covered by this retirement system but who was not eligible for membership in this retirement system on July 1, 1998, may make an irrevocable election to become a member by so notifying the board of trustees not later than December 31, 2000. Any such person shall be credited with service in this retirement system only for actual service in such position. The Employees' Retirement System of Georgia shall transfer to this retirement system all employer and employee contributions paid by or on behalf of any such member with regular interest thereon. The member is authorized, but not required, to pay to the board of trustees such additional amount as the member desires, each payment to be made within 12 months of electing to become a member of this retirement system. Such member shall receive only such creditable service, not to exceed the actual years of service, as that amount will warrant without creating any actuarial accrued unfunded liability to this retirement system calculated as if the member had either elected or rejected spouse's survivors benefits at the member's option.