Revenue bonds at any time issued by a municipality (a) for the purpose of enlarging, improving or expanding any manufacturing, industrial or commercial project then owned by such municipality and acquired by it pursuant to the provisions of Act No. 756 enacted at the 1951 regular session of the legislature of Alabama as heretofore amended, or (b) for the combined purpose of so enlarging, improving or expanding any such project and of refunding any revenue bonds theretofore issued by it under said Act 756, shall not be deemed to constitute bonds or indebtedness of such municipality within the meaning of sections 222 and 225 of this Constitution if by their terms such bonds are not made a charge on the general credit or tax revenues of the issuing municipality and are made payable solely out of revenues to be derived by such municipality from the leasing of such project as so enlarged, improved or expanded. Each municipality in the state is hereby authorized so to issue such revenue bonds, for either or both such purposes, at any time and from time to time and on the same terms and conditions, with the necessary changes in details, as prescribed in said Act No. 756 for the issuance of revenue bonds for the purpose of acquiring such a project, anything in the Constitution of this state or in said Act No. 756 to the contrary notwithstanding.