(1) The interest and principal of such bonds is payable in the United States, or with exchange to a city in the United States, in lawful money of the United States or its equivalent; and
(2) The bonds at the time of purchase pursuant to the authority of this section are rated in one of the four highest grades by a rating organization recognized in the United States that has been regularly engaged for a period of 10 years or more in rating or grading bonds. [1959 c.185 §3; 1977 c.135 §35]