Notwithstanding the provisions of Kan. Stat. Ann. §§ 74-4913 to the contrary, an employee who became a member of the Kansas public employees retirement system on June 1, 1969, and who was first employed by the same participating employer from December 1, 1957 to July 19, 1961, shall be entitled to receive upon retirement prior service credit for such employment prior to January 1, 1962. The prior service benefit for such employee shall be computed by using a prior service salary of five thousand five hundred sixty-eight dollars ($5,568).