Any part of a fuel tank or container or intake pipe shall not be located within or above the passenger-carrying portion of a school bus unless securely sealed off from that portion by means of a substantial metal cover. Fuel lines shall not extend above the frame rails. The gasoline container, including intake pipe, cap and vent on a school bus manufactured subsequent to December 31, 1964, shall be so designed that, in the event of overturn, the fuel will not be spilled at a rate in excess of 1 ounce per minute.