Notwithstanding the provisions of Kan. Stat. Ann. §§ 74-4913 to the contrary, an employee who became a member of the Kansas public employees retirement system on October 1, 1968, and who was first employed by another participating employer from December 10, 1947, through January 28, 1967, shall upon retirement be entitled to receive prior service credit for such employment prior to January 29, 1967. The prior service benefit shall be computed by using a prior service annual salary of four thousand two hundred ninety-one dollars ($4,291).