Contact Johns Draxler at thunderbird ranch in Pittsville Wi.
He has a very extensive website and should be able to help.
I am of the opinion before you spend lots of time doing this sort of welding job, you need to evaluate the bird to see how bad the rust underneath really is. If your bird has gone this far and is flexing when on the ground you have major rust issues that would in my opinion make the bird a canidate for becomming a parts car. I don't say this likely but in order to bring back to .life you will need to find a donor can and steal lost of metal from that bird.
I know John has brlought back cars from the dead so he is your best source of info.
Sun Prairie, Wi.
PS If you do decide to try and save the bird, and it is a 58, I might have some decent sheet metal from cars that are no longer restorable for a variety of reasons.