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.
OldSub
This truck being it's a 1 ton doesn't have the X-member like the 1/2 tons.
I think it's called a ladder style frame.
I bought a 69 auto trans crossmember off eBay because the measurements seller took seem to be pretty darn close to bolting right into my 61's frame.
(My drivetrain is a 2 speed O/D bolted in front of an SM465 w/ parking brake.
It's longer than OEM and would have run into torsion bar crossmember. Nobody thinks I should hang all that off the bellhousing - so the truck gets a trans crossmember.)
I think bolting the bellhousing/motormount crossmember back in temporarily is probably good enough.
Thanks
Pete
