The principal and interest of the bonds shall be payable:
(a) First, out of the revenue derived from the operation of the project or projects for which the bond proceeds were or are to be used or expended, or any other revenues derived from said project;
(b) Second, from such other revenues, including existing funds, of the entity as are described or stated as security for the bonds in the indenture in accordance with Section 6549 hereof.
(Amended by Stats. 1957, Ch. 943.)