Sometime you don’t know how good or bad the frame is until you pick the body up to get a better look. There is another member on this site that has a VERY nice 71 that was a frame-on resto. Last fall,he had to repair a rusted fuel line and found rot holes in his frame. Now he has to carefully take the car apart,and swap the frame for a nice one. The paint job alone was $15k,so he’s gotta be real careful.
Geez, that wouldn't be much fun. I actually just had all my fuel lines from the tank to the font replaced. I also had some body mounts changed and the frame inspected at that point as well. I had the passenger side torque box replaced a few months ago. My mechanic is very good at metal fab repair. The frame rails are good, but I am going to get them boxed in this winter as the car is 53 years old and did go through some Canadian winters. I'm doing upgrades/restoration as I go.