No retail installment contract shall be signed by any party thereto when it contains blank spaces to be filled in after it has been signed except that, if delivery of the motor vehicle is not made at the time of the execution of the contract, the identifying number or marks or similar information and the due dates of the installments may be inserted in the contract after its execution, and except that the contract may be so signed provided the buyer is given at the time of the execution a bill of sale, invoice or similar memorandum clearly indicating the cash sale price, the gross down payment and the types of insurance coverage. The buyer’s written acknowledgment, conforming to the requirements of subsection 4 of section 365.070, of delivery of a copy of a contract shall be conclusive proof of the delivery, that the contract when signed did not contain any blank spaces except as herein provided, and of compliance with section 365.070 in any action or proceeding by or against a holder of the contract without knowledge to the contrary when he purchased the contract.