floor pan firewall question

You can get the floor pans new. If its just a few inches in front of that it is not too difficult to bend pieces to weld in. If much more than that you may need a firewall or at least doner section and are getting beyond a' beginners scope of work' and into the 'is it worth it' question. Also can't see in your pic where you cut side or back to know if too far for new pan to cover. Most of these can just be overlapped, since you wont see them. I usually use a pnuematic flange tool where I need to level the metal, not important on a floor pan though. I would not try to butt weld anything there unless you are a really skilled welder trying to do a perfect restoration. Be sure to seal everything from underneath. I used Black Jack neoprene for that (regular seam sealer inside)