GM use to make a full floor. They are scarce these days. I got one at dealer cost in 98 and it was close to $500. I'd say call the dealer and ask if there are any in warehouses.
The half panels wont do you much good unless only half the floor has a hole. The supports on the under would have to be saved somehow. If you where going to piece in sections I would think you would have to cut out the rusty spots and lay the other metal over the top. I didn't like that idea since most of the supports in my project truck where rusted through, so I ripped it all out and started from scratch with a subframe and all that jazz. I have a ton of pics in the body shop but its not for everyone... I had a little bit of money and a lot of time /forums/images/graemlins/deal.gif /forums/images/graemlins/rolleyes.gif