Refunding bonds issued under the provisions of sections 108.400 to 108.410 shall make reference to sections 108.400 to 108.410 and, except as otherwise provided by sections 108.400 to 108.410, may become due in not to exceed twenty years from the date thereof. The bonds shall be in such denomination, bear such rate or rates of interest, not exceeding the average rate borne by the bonds being refunded, be payable at such place or places, and contain such redemption privileges as may be specified in the ordinance, order, or resolution authorizing the bonds.