All persons who were on June 30, 1975, entitled to a service retirement pension or disability retirement pension, under this Fund or any fund of which this Fund is a continuation, and who meet the conditions prescribed hereinafter, shall receive supplementary payments as follows:
     (1) In the case of any such retired person, who attained or shall attain after June 30, 1975, the age of 60 years, who was in receipt of a service retirement pension, the payment pursuant to this section shall be an amount equal to the difference between (a) his annual service retirement pension from the Fund plus any annual payment received under the provisions of Section 34-87 (now repealed) of “The School Code”, approved March 18, 1961, as amended, if the total of such amounts is less than $4500 per year, and (b) an amount equal to $100 for each year of validated teaching service forming the basis of the service retirement pension up to a maximum of 45 years of such service;
     (2) In the case of any such retired person, who was in receipt on June 30, 1975, of a disability retirement pension, the payment shall be equal to the difference between (a) his total annual disability retirement pension and (b) an amount equal to $100 for each year of validated teaching service forming the basis of the disability retirement pension.