That "tub" that's welded to the floor doesn't do much for integrity of the cab. It's just spot welded and is for support for the seat, not strengthening of the cab. On mine (and my dad's 52) we just ground them out with an angle grinder and a cut off wheel. Make sure you wear full coveralls, safety GOGGLES (not just glasses), and ear protection. It's both loud in there and there are a ton of sparks flying around.
No extra bracing is needed after your remove it.
