So maybe this is a stupid idea, but why relocate the gas tank(s)? why not section the tanks so that they fit under the new flat floor? You would probably only lose a few gallons of capacity and you can get a gas tank cleaner/resealing kit for about $40. You can just mark the tanks to clear the area you cut out for the new floor pans, drop the tanks, wash them out thoroughly and then cut them while full of water(just in case) and then weld in flat plate to clear the new pan. Once you are done, you can clean and reseal the tank with something like an Eastwood Gas Tank Sealer Kit. I think all of the important filler and sending unit bits are in different areas, so that shouldn't be a concern right? Even with dual tanks it would still be cheaper than getting a new single blazer fuel tank.
