Section 55. From time to time, the department shall certify to the comptroller, and the state treasurer shall, within thirty days after each such certification, pay to the several cities and towns, from any amounts appropriated therefor, the amounts due them in accordance with the following clauses:—
(a) Certification may be made only of projects with respect to which contracts for federal capital grants under Title I of the Federal Housing Act of 1949, as amended, have been signed.
(b) The total urban renewal assistance grant for any approved federally-aided project as defined in clause (a) shall not exceed one half of the local share of the contribution required from the municipality under the federal capital grant contract or more than one sixth of the net project cost when the municipality pays for administrative planning and legal expenses as a part of the gross project cost.
(c) The total urban renewal assistance grant to be paid under the provisions of this section shall be payable in twenty equal annual installments, except that the department may adjust the annual payment upon final determination of the net cost of each approved project.
(d) The total amount of urban renewal assistance grants to be paid under this section shall not exceed $4,500,000 in any one fiscal year or a total of $70,000,000 in the aggregate.