Notwithstanding the provisions of Kan. Stat. Ann. §§ 74-4913 to the contrary, any employee of a participating employer who became a member of the Kansas public employees retirement system on January 1, 1968 who was previously employed periodically by said participating employer from November of 1951 through December of 1966 shall upon retirement be granted prior service credit for all service with said employer prior to January 1, 1968. The prior service benefit shall be computed by using a prior service annual salary of two thousand eight hundred sixty-eight dollars and fifty-six cents ($2,868.56).