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 June 1, 1974, and who was previously employed by said employer from March 1, 1941 through December 31, 1957 shall upon retirement be granted prior service credit for all service with said employer prior to January 1, 1963. The prior service benefit shall be computed by using a prior service annual salary of two thousand five hundred and fifty-six dollars ($2,556).