The proceeds from the sale of the bonds shall be paid out or disbursed solely for the acquisition or construction of the toll tunnel, the acquisition of the necessary lands and easements therefor, and the payment of interest on the bonds during the period of actual construction and for a period of six months thereafter, only as the need therefor arises. The authority may agree with the purchaser of the bonds upon any conditions or limitations restricting the disbursement of such funds which are deemed advisable for the purposes of assuring the proper application of the funds.