The manufacturer shall establish that binding purchase contracts have been executed satisfactory to the Secretary providing for the purchase and delivery of the houses to be manufactured, which contracts shall provide for the payment of the purchase price at such time as may be agreed to by the parties thereto, but, in no event, shall the purchase price be payable on a date in excess of thirty days after the date of delivery of such houses, unless not less than 20 per centum of such purchase price is paid on or before the date of delivery and the lender has accepted and discounted or has agreed to accept and discount, pursuant to subsection (i) of this section a promissory note or notes, executed by the purchaser, representing the unpaid portion of such purchase price, in which event such unpaid portion of the purchase price may be payable on a date not in excess of one hundred and eighty days from the date of delivery of such houses;

Such houses to be manufactured shall meet such requirements of sound quality, durability, livability, and safety as may be prescribed by the Secretary;

The borrower shall establish to the satisfaction of the Secretary that he has or will have adequate plant facilities, sufficient capital funds, taking into account the loan applied for, and the experience necessary, to achieve the required production schedule;

The loan shall involve a principal obligation in an amount not to exceed 90 per centum of the amount which the Secretary estimates will be the necessary current cost, exclusive of profit, of manufacturing the houses, which are the subject of such purchase contracts assigned to secure the loan, less any sums paid by the purchaser under said purchase contracts prior to the assignment thereof. The loan shall be secured by an assignment of the aforesaid purchase contracts and of all sums payable thereunder on or after the date of such assignment, with the right in the assignee to proceed against such security in case of default as provided in the assignment, which assignment shall be in such form and contain such terms and conditions, as may be prescribed by the Secretary; and the Secretary may require such other agreements and undertakings to further secure the loan as he may determine, including the right, in case of default or at any time necessary to protect the lender, to compel delivery to the lender of any houses then owned and in the possession of the borrower. The loan shall have a maturity not in excess of one year from the date of the note, except that any such loan may be refinanced and extended in accordance with such terms and conditions as the Secretary may prescribe for an additional term not to exceed one year, and shall bear interest (exclusive of premium charges for insurance) at not to exceed 4 per centum per annum on the amount of the principal obligation outstanding at any time.