Easiest way to to this is to put some grease on the tank bungs and put the tank in after the new floor is in. This is what I did on my '53 and it worked great.
You might want to wait until you have the new floor and the tank you will eventually use, as some of the new tanks don't exactly match the original locations.
Would someone be willing to provide me with a couple of measurements for the locations of the two floorboard holes for the gas tank? I have the old flooring as a template for the size of the holes, but not their positioning relative to the back or side of the jeep. (Yes, I know hat I should have thought of this prior to hacking everything up. Not the first time.) Thanks.