I made my own floor raplacement panel but thankfully I didn't have to replace the rail too. If after you have removed the rail you can flatten it (may require cutting on formed corners) you can make a template on cardboard. You may be forced to only make something "similar" but I'd think if you follow the general principles you should be OK. As with all mods, "Do at your own risk."
Below is an image of the replacement panel. I put dimples in to strengthen the flat metal. I simply used a larger socket on the bottom and a smaller one up top. If you notice some are missing. Ahh..., yea, when it all slips, you smash your finger..., you say "enough is enough." None of it is pretty, but it is all under carpet. The two parallel rows are where the floor was plug welded to the frame rail.