Welding lots of slugs in the frame doesn't sound like fun when better frames are not that hard to find.
But if he's swapping engines for a newer diesel the front clip comes off. The bed is already off. He'll need a different rear axle. The steering box comes out to replace with a PS gear box.
At this point he's got a few wires, clutch and brake pedal and 4 bolts holding the cab on, it would be really easy to swap the frame for a better one.
Or he did say this is his only truck, in which case if it runs and drives as is use it for now while building the diesel one on another frame, then swap the sheet metal later on.
Grigg
I use the city bus for now, the truck does not run the radiator is blown, the engines has problems and the starter or alternator went out and since I work from home time is not the issue. The issue is I am new to restoring trucks. Mine is down to a bare cab sitting on the original frame, then the engine and tranny are still in.
