You would be better off doing a built 4.3 Vortec swap, it will fit easier, lighter, and are common enough that virtually every thing you need you can buy from one outfit or another. I don't think the stock torsion bars will support the weight or clear the 350 even w/susp. lift, an SAS and BL will also be needed.

You might also consider a Supra straight six swap, same benefit but less weight and less headaches. If you found you still needed more power you could always bolt on a turbo or two. <img src="/forums/images/graemlins/kewl.gif" alt="" />

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed