I have moved your question to a new topic so as not to derail GMCNut's thread. Some potential problem areas in which to look are as follows:
- Cab Corner Rust
- Broken Light Bezels
- Body Filler (Knock on panels to locate)
- Heavy Oil Leaks
- Knocking Engine
- Chopped or rerouted wiring
- Chopped Radio Holes in Dash
- Wobbles in Steering
Others will follow with more, however in the end the answer to your question lies in what kind of work you would be willing to put into a 50 year old classic. Above all, remember that this is not a Chevy, available on every street corner. It is becoming more of a rarity every day.
Best of luck!
-Jeannie
6066 GMC Club