Check for rust around the back window. Mainly the bottom corners where water would settle and begin to rust. Also open the trunk and looks up into those areas and the package tray area from inside the trunk. Reach down into the quarter panels inside the trunk and check for rust, bondo, or fiberglass repairs.
I have a 70, not much differance where they rust. I had to replace. Floor pan under back seat it was rusted on top of the frame and just looking under the car on the ground I couldnt see it. Then I got it home up on a lift and seen it rusted above the frame. Also had to replace the entire section behind the back window, and the trunk floor. Check for rust around front windshield also. I can nearly bet the sides of the cowl are rusty also and you cant see this with a fender on it. Years and years of debris like leaves get trapped down in there and rot that out.
Hope shes a good one for you.