Any active and contributing member of the Employees’ Retirement System who has vested retirement benefits may hereby claim and purchase credit in the Employees’ Retirement System for up to four years’ time for employment by the Alabama Legislature prior to 1979, provided, that such member shall pay into the Employees’ Retirement System the total amount he would have contributed had he been allowed to contribute at the position and salary level, together with interest not to exceed eight percent compounded annually from the date of service to the date of payment, and provided that he shall make such payment within one year from May 19, 1989.