I'm pretty sure this truck is the parts hauler owned by the guy responsible for the '74 Buick LeSabre, Studebaker Avanti, '69 Buick Electra, '65 Ford Ranchero, and '69 Cadillac Coupe de Ville convertible. Each of those cars lived on the block for a few months, then disappeared, so most likely this is a serious car guy who wheels and deals at all times. And for that you need a big pickup!
The 240-cube six was the base engine for 1966 Ford light-duty pickups, but the dual exhausts on this one suggest that it has some sort of V8. The 352 was the optional powerplant for this truck in '66, but odds are good that a larger member of the FE family now lives under the hood. 390? 428?