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, who was first employed by another participating employer from December 1, 1950, to February 18, 1951, and was again employed by the same employer from January 1, 1952, to April 4, 1953, and was again employed by the same employer from August 31, 1954, to May 23, 1956, shall upon retirement be entitled to receive prior service credit for such employment prior to January 1, 1963. The prior service benefit shall be computed by using a prior service annual salary of four thousand eight hundred dollars ($4,800).