Welcome, you've found the best place on the net for c-bodies. Congratulations, that's very cool that you got the car, thanks for saving this one. It'll be interesting what you find with it, there's always a lot of speculation on this site about cars for sale and it's always nice if we find out the real story. The cars are often better than judged/expected on this site. C-bodies that are reasonably well taken car of, usually hold up very well because they're very sturdy cars, there's a reason most police departments used C-Bodies from the mid 60's through the mid 70's.
FYI, The normal problem areas are rust under the vinyl top around the rear window, windshield, and top of the C-Pillar. Also the trunk pan will be rusty if the rear window has rust around it and vice/versa.
Keep us posted, there is a lot of great advice and inexpensive parts available on this site.