Whenever the Secretary of Defense or his designee determines that it is desirable in order to effectuate the purposes of this title, the Secretary is authorized, without regard to the civil service and classification laws, to procure, by negotiation or otherwise, the services of architects and engineers, or organizations thereof, under such arrangements as he deems desirable, but at an expense not in excess of that permissible under the schedule of fees allowed from time to time by the Secretary of Housing and Urban Development in connection with projects assisted under the United States Housing Act of 1937, as amended [42 U.S.C. 1437 et seq.]. Such services may include the development of plans, drawings and specifications for family housing under this title and other services in connection therewith: Provided, That such plans, drawings, and specifications may include the use of any project to be constructed under this subchapter of alternate materials or alternate types of construction, including prefabrication, that provide substantially equal value and conform to standards established by the Secretary of Housing and Urban Development: Provided further, That such plans, drawings, and specifications, when developed pursuant to arrangements made under this section after August 7, 1956, shall follow the principle of modular measure, in order that the housing may be built by conventional construction, on-site fabrication, factory precutting, factory fabrication, or any combination of these construction methods: Provided further, That the Secretary of Defense may designate certain sites or parts thereof for family housing to be furnished from prefabricated houses or housing components. Such arrangements may include provision for advance or progress payments, for payment by third parties, for payment by the Government of any such compensation as it not paid for by third parties, and shall include provision for reimbursement by third parties to the Government of any compensation or other expenses paid by the Government pursuant to this section, and may include other provisions for compensation. Any public works appropriations now or hereafter available to the Departments of the Army, Navy, or Air Force or the Coast Guard may be obligated by the respective departments or the Coast Guard for these purposes. Reimbursements to the Government on account of payments made pursuant to this section shall be made to appropriations against which such payments were charged. The Secretary of Defense is further authorized to advance or pay to the Department of Housing and Urban Development its “Appraisal and Eligibility Statement” fees in connection with such family housing. The Secretary of De