In all Class 1 municipalities, notwithstanding any provision to the contrary in any section of Article VI of Act No. 929, S. 676, Regular Session 1951 (Acts 1951, p. 1579), as amended, any benefit payable on a monthly basis to a participant or retiree under Act No. 929, S. 676, Regular Session 1951 (Acts 1951, p. 1579), as amended, shall not be of an amount less than $400.00 per month, and any survivor’s or spouse’s benefit payable on a monthly basis shall not be of an amount less than $160.00 per month.