Notwithstanding the provisions of Kan. Stat. Ann. §§ 74-4913 to the contrary, an employee of a participating employer who became a member of the Kansas public employees retirement system on February 1, 1963, who was employed by said participating employer on January 23, 1950 until July 10, 1957, shall upon retirement be granted prior service credit for all service with a participating employer prior to January 1, 1962. The prior service benefit shall be computed by using a prior service annual salary of four thousand two hundred ninety-six dollars ($4,296.00).