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 February 1, 1963, who was first employed by said participating employer on January 15, 1962, who was previously periodically employed between September, 1940 and January 13, 1962, by several participating employers whose entry date was January 1, 1971, shall upon retirement be granted prior service credit for employment with said participating employers prior to January 1, 1962, whether such employment was continuous or not. A prior service benefit shall be computed by using a prior service annual salary of three thousand five hundred ten dollars ($3,510).