Notwithstanding the provisions of Kan. Stat. Ann. §§ 74-4913 to the contrary, any employee of a participating employer with an entry date of January 1, 1962, who became a member of the Kansas public employees retirement system on March 1, 1966, who was employed by such participating employer on January 21, 1957, until February 6, 1961, shall upon retirement be entitled to receive prior service credit for employment from January 21, 1957, until February 6, 1961. The prior service benefit will be computed by using a prior service annual salary of four thousand three hundred and five dollars ($4,305).