[gordon]

I think it has started life as a panel van, or more likely a K-51 ( that's one of those odd cases where they built a batch of vans, then contractor-converted more of them to K-51 than they left as plain panels, so plain panel vans now rarer)

Reasonably certain it was never a bomb tractor, as it is the longer standard wheelbase ( unless someone has stretched it ) instead they have cut off most of the body, split the cab rear centre, and pushed the back corners apart, then filled in the gap - not uncommon where you wanted to widen the cab to take a three person seat. Hinging screen has been taken out and lobbed / welded / glued back in.

Zero chance of finding a panel body pretty much anywhere. If the mechanicals are intact, bin the cab and fit a standard GMC / Chev truck cab, keep the front metal, and buy a 1.5 ton standard Budd cargo body for it.