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 January 1, 1971, who was employed by said participating employer on January 14, 1963 to January 9, 1967, shall upon retirement be granted prior service credit for all service with a participating employer prior to January 1, 1971. A prior service benefit shall be computed by using a prior service annual salary of six thousand five hundred fifty-nine dollars ($6,559.00).