Notwithstanding the provisions of Kan. Stat. Ann. §§ 74-4911 and 74-4913 to the contrary, an employee of a participating employer who was employed by said employer on October 1, 1969, and who was employed by another participating employer from January 1, 1963 until June 30, 1967, and who is employed by a participating employer on the effective date of this act, shall be an eligible member of the Kansas public employees retirement system as of January 1, 1963, upon the payment of appropriate employer and employee contributions, and shall be entitled to receive participating service credit for employment with the participating employer from date of membership. Said employee shall also be granted prior service credit from June 17, 1957, until July 31, 1959. The prior service benefit shall be computed by using a prior service annual salary of two thousand six hundred sixty-four dollars ($2,664).