Hi and welcome to Fordbarn.
You have asked a very open ended question to which about a million answers would all be correct. could you please tell us a bit more about what you are wanting to do?
Off the top of my head, I would go for a 39/40 car or 39/40/41 pu frame. This is the same as a 35 pickup (in essence) but already has hydraulic brakes and better steering box. Once your cab is fitted, you would need a new pickup bed and the correct front sheetmetal. I don't know how much of the front end sheetmetal is the same as the pickup, you have the truck, what are your thoughts??
Mart.