I'll second wht TrackVino said about time and money.  Your money tree had better be in full bloom when you start a 4.3 swap unless you're incredibly resourceful at getting free labor and parts.  Mine snowballed on me until it wasn't just a motor swap and 1 year later I still have loose ends that haven't been resolved.  If you're building a crawler, stick with the 22RE plan and dual case it for the gear reduction.  Just my