That's great work.
That's a really neat weld on the fuel tank well to the old floor!
I see you're using only enough of the new floor to replace the rusted section of the old, keeping original what's not rusted. That's how I'd do it, too.
A question: it appears in the pictures that you have the new flooring section 'underlapped', for want of a better word, to the old flooring, but are butt welding it on the other side (the correct way, of course). Are you trimming the new floor to the size of the opening as you go, and if so, how are you doing it? I can't think of a tool that would allow you to do that, or how it could be done. Maybe the picture is deceiving and you have actually trimmed the new panel to the correct size.
I'm really interested to know how you're doing it.
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt"..Bertrand Russell