Any instrumentality jointly created by this state and any other state or states is hereby authorized, upon the granting of like authority by such other state or states, (a) to enter into an agreement with the secretary of health, education, and welfare whereby the benefits of the federal old-age and survivors insurance system shall be extended to employees of such instrumentality, (b) to require its employees to pay (and for that purpose to deduct from their wages) contributions equal to the amounts which they would be required to pay under section 5 if they were covered by an agreement made pursuant to section 3, and (c) to make payments to the secretary of the treasury in accordance with such agreement, including payments from its own funds, and otherwise to comply with such agreements. Such agreement shall, to the extent practicable, be consistent with the terms and provisions of section 3 and other provisions of this act.