I am going to be a bit negative. Don't think of this as a lottery where you can win a "dream car" Go planning to have to negotiate or turn the deal down. At inspection time bring a magnet and check the obvious spots, fender wells, trunk drop offs, rockers, etc. The floor is tough unless you can get under the car, carpet hides a lot. Rust on the top of the dash in the corners is a pain to fix. The suspension is usually shot, cracked control arm bushings, worn ball joints etc. I find electrical a PITA. That being said if you can bolt it on to fix it great. If you have to cut, weld and modify it will get expensive and demotivating quickly. If the body is solid, the frame and body mounts are solid, and all of the electrical systems work well you are off to a good start. For 20k it will need work. Interior parts can be expensive, the deluxe door panels I need are $400 and I have to transfer parts from the old panels.
Ask a lot of questions, request a lot of pictures, check prices to fix what you do not like, 20K is not an impulse buy.
Youtube videos I've made, a couple of Firstgens vids included.http://www.youtube.com/user/dons69camaro
“I have never in my life learned anything from any man who agreed with me.”
- Dudley Field Malone