OK, so front mud flaps were a complete failure. On the left side, my plan worked perfectly. I got the previous screws/rivnuts out, and was ready to go. The problem was the right side. The outrigger simply had too much rust. As I started trying to break the screw, the rust hole got larger, and one of the screws "folded in" I stopped before I really broke something.
Other than the outriggers, the frame looks fairly good. The rear crossmember was replaced before I bought it, and while there is some surface rust, I think I can clean that up and repaint. The front scares me a little, as there is some rust where the bumper meets, but it's not an emergency. I see outriggers are available, but would have to hire that out, and I think I'd be overwhelmed by labor costs, as it looks like the wings would have to come off, and something done with the bulkhead mounts as well. I'm at a loss with that, and if anyone has info on the process, it would be very much appreciated!