I just finished putting new floor pans and floor supports in my 75 CJ5 , that I got from Classic. They fit great and are heavier gauge metal than stock. They are a bit over sized so you can trim them to fit. And the guy at Classic was very helpful when I called.
I already had the tub off when I did mine because I'm doing a complete rebuild. But, based on what I had to do to get the old pans cut out and the new pans fit and welded in, I would say that you would be saving yourself a whole lot of grief in the long run by biting the bullet and pulling the tub.