The refunding bonds shall be of such form and denomination, payable at such place, bear such date, and be executed by such officials as may be provided by the highway commissioner and the road district clerk of the road district in the bond resolution. They shall mature within not to exceed 20 years from their date, and may be made callable on any interest payment date at par and accrued interest after notice has been given at the time and in the manner provided in the bond resolution.
     If there is no default in payment of the principal of or interest upon the refunding bonds, and there is sufficient money on hand to set aside a sum of money equal to the amount of interest that will accrue on the refunding bonds, and a sum of money equal to the amount of principal that will become due thereon, within the next 6 months period, the treasurer of the road district shall use the money available from the proceeds of taxes levied for the payment of the refunding bonds in calling them for payment, if, by their terms, they are subject to redemption. However, a road district may provide in the bond resolution that, whenever the road district is not in default in payment of the principal of or interest upon the refunding bonds and has set aside the sums of money provided in this paragraph for interest accruing and principal maturing within the next 6 months period, the money available from the proceeds of taxes levied for the payment of refunding bonds shall be first used in the purchase of the refunding bonds at the lowest price obtainable, but not to exceed their par value and accrued interest, after sealed tenders for their purchase have been advertised for as may be directed by the corporate authorities thereof.
     Refunding bonds called for payment and paid or purchased under this section shall be marked paid and cancelled.