Notwithstanding the provisions of Kan. Stat. Ann. §§ 74-4913 to the contrary, any employee of a county who became a member of the Kansas public employees retirement system on April 1, 1964, and who was employed by other participating employers periodically from January, 1947, until November 30, 1960, shall upon retirement be granted prior service credit for all service with all participating employers prior to January 1, 1962. The prior service benefit shall be computed by using a prior service annual salary of four thousand one hundred seventy-two dollars and fifty cents ($4,172.50).