There are alot of "40" Ford pkps running around that were built using later cabs from either pkps or old large Ford cabs... all cabs were essentially the same. As I understand it, a true 40 pickup did not have a headliner, did have the raised dash area, and did not have the hole in the cab for a gas filler tube that went to a tank under the seat. Use the best cab available on a 35-40 chassis and "keep working!"