WOW! A station wagon with a rag-top and "messed up exhaust" ??? Isn't that enough?

LOL!
I think you must mean a vinyl top....
Cause there's no rag top Caprice's since the late 70's
There's really nothing secific to "look for"...if the owner did the necessary maintenance on the car you'll be fine.
It's always best to take a car you're interested in buying to a mechanic that you trust and let him go over it thoroughly. It's good insurance. Hope it works out for you!