I think you saw the pictures of how I totally disassembled my 1974 Cuda.
It will all come apart like Steve says, I drilled out every spot weld.
Would not wish that on anyone to have to go as far as I had to on mine.
If I had to do it again (which I will on my other 1974) I will only replace what has to be replaced.
It is not necessary to replace a whole panel, to get rid of the rust, identify it, cut it out, make a piece and put it in, take lots, and lots of time welding it upp, smoothing it out, working it.