I've read that section before:
I would've expected the condition of a new floor to be such that it didn't come pre-sagged, but who knows with the way they handle the deliveries on these things. The goal at the moment is to figure out where it's malformed to be able to put it back to approximately where it needs to be to avoid any other further problemsThe final minor adjustment that could be necessary is in the rear foot well near the drive shaft tunnel. This metal is very close to the inside frame support. The condition of your floor will determine whether it will come into contact with the new replacement frame. It is a good idea to glue a small strip of rubber to the top of the frame in this area to keep the body and frame from rubbing.