Any participant who served as a Village Trustee, and was not then eligible to participate in the Illinois Municipal Retirement Fund for such service, may elect to receive credit under this Article for such service by paying to the Fund: (1) an amount equal to his annual salary at the time of election, times the employee contribution rate in effect at the time of election, times the number of years of service credit to be granted under this Section; plus (2) an amount equal to his annual salary at the time of election, times the employer contribution rate in effect at the time of election, times the number of years of service credit to be granted under this Section. The service credit received under this Section may not exceed 50% of the participant’s service credit in the Fund at the time of election. No person may receive more than 4 years of service credit under this Section.