In any municipality with a population under 10,000 that is located in a county with a population over 3,000,000 and that maintains a firefighters’ pension fund under Article 4 of the Illinois Pension Code, persons who participate in that pension fund and who have served at any time between July 1, 1976 and July 1, 1978 in the position of protective inspection officer or administrative assistant for fire services shall, if the position included firefighting duties, be entitled to receive service credit in that pension fund for such service, notwithstanding that such persons may not have held civil service appointments as firefighters, provided that application is made to the pension fund by July 1, 1992, and the corresponding employee contributions are paid, based on the compensation received for such service and the contribution rates in effect during such service for firefighters in the pension fund, plus interest thereon at the rate of 6% per year, compounded annually, from July 1, 1988 to the date of payment.