I'm not real familiar with the structure of the torsion bar frames, so I don't have a good sense for how much it might move. If you feel its at all loose then yes I'd suggest putting in some supports before taking it apart.

The later frames seem pretty stiff to me, and I would not be worried about one of those while making a crossmember swap.

1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble...