Hey guy, frame opinion...

I got an original "ebay ripoff" special! A 69 Formula S Fastback big 383 4spd that had "solid frame rails" from PA. When we got a good look underneath, it was full of cancer. Had to replace the entire front clip, firewall & all. Saved my radiator support w/ VIN. We have to replace the rear rails due to accident damage & found more rust had weakened the outer floor. I decided to move the rails in 2" on each side & add 2" to each inner fender well & will hopefully, get a 10" rim & 12" section width of tire completely inside w/ inches to spare. I plan to lower the Cuda & put Cal Track Mono Leafs & coil overs to hook it up.
Many said not to modify it, but in reality, what collector would buy a car that has had so much of it replaced due to rust?
Point is that a rusty car will always have that stigma attached to it. If I had it to do all over again, I'd sell the cuda as is & put the $40K into a solid car that is rust free. I couldn't bear to see this all original Formula S be scrapped or rebodied & my love for the rare Cudas overpowered any wisdom that was rollin around upstairs.
I got a rust free 70 T/A in the garage that I'm getting ready for paint. The $30K I've already got into the rusty Cuda would've finished the T/A.
I admire your zeal & wish you the best if you decide to tackle the project, but consider what the same money, labor & time could do w/ a rust free car.