After letting it sit for nearly a year, I finally decided to get back to work on the car. I started by stripping the "paint" from the quarter panels, roof, and rear panel, using a combination of aircraft stripper, putty knives, and roloc wheels.

It appears that the cause of the rust was primarily an (old) collision repair. It looks like the car was hit fairly hard in the left rear corner many moons ago (when it had the original paint), the panel was pulled, and bondo generously applied. The panel rotted behind the bondo. Dents in the rear panel support the rear collision theory (look to the right of the gas filler neck).

After seeing all the rust in the quarter panel, I decided to cut into things to see how far the damage went. The answer was: pretty damned far. The lower trunk filler panel was missing about two inches of metal, and the bottom of the outer wheelhouse panel was, uh, mostly gone. To be fair, there was probably 1/64" of rusty steel left under 1/8" of bondo.

After seeing all that damage, it was fairly obvious that major repairs were in order, so I started stripping the interior and removed the rear window, before calling it a day, because it was getting dark.