Rule of thumb, if the doors still open & close correctly, its still pretty sound, structure wise. If it wasn't a big deal to get it running, I might be tempted to drive it for a year or 2.

Back in high school, a couple of my buddies hacked the roof off of a 67 or 68 Chrysler. They beat the crap out of it the first summer, I remember at least 9 people piled in in on more then 1 occasion. The second summer, the doors didn't work well, so they welded the doors shut and ran it another summer. Of course that 68 Chrysler was only 6 or 7 years old at the time, but I remember it had rusty quarters, so it wasn't a prize to begin with.

Have fun with it, then part it out & build your couch. Gene