Any municipality, which has obtained authority prior to March 3, 1933, to issue and sell bonds for the construction and installation of any of the improvements mentioned in this chapter may defray the cost of such improvements entirely out of the proceeds of the sale of such bonds, or it may defray the cost of such improvement in part out of the proceeds of the sale of such general liability bonds and in part out of the proceeds of the sale of mortgage bonds as provided in this chapter, except that the mortgage indebtedness upon such improvement, when the same is created originally, shall not exceed three-fifths of the total cost of such improvement. Bonds issued under this section which are a general liability of the municipality shall not be issued except upon a vote of the people as provided in chapter 21-03.