Given the ever-escalating costs of paint and bodywork, it might pay rust belt residents to travel to less corrosive parts of the country in search of a good body. Buying a long-distance truck and shipping or towing it home may seem like a big expense, but do the math. It doesn't take too much professional rust repair to xceed the cost of even cross-country shipping in a deluxe enclosed carrier.
Since you're building a street rod truck, we wouldn't be concerned about the condition of the engine, transmission, rearend, or chassis components. The only possible chassis problem would be one that was so decrepit that it had sagged and caused the cab to twist. The door fit and gap uniformity weren't all that great when the trucks were brand new.
The original chassis, engine, and transmission were in excellent condition on the RB's '47 Chevy panel, so the package was easily sold to a restorer. Selling off unneeded stock parts is a way to recoup some of the initial investment, but there doesn't seem to be a huge demand for old Stovebolt engines and three-speed manual transmissions.
The accompanying photos show the starting point of the Urban Suburban and, as some good background material, highlight some of the differences among the various years of the '47-54 GM trucks. Check this out and look for some more in-depth coverage next month.