agreed, you'd only need 1/4-1/2" so the torsion bars will be fine. to check just loosen the bolts and slip in some c shaped plywood spacers. once you know it works make up some steel spacers, remove one bolt at a time and fit them. if the trans needs lowering slot the crossmember bolts til you're happy then weld washers to it to cover the slots.
it's only metal, lol.
neil.