On an A-body there's really no point in doing a full 3" spring relocation to the frame rails without also doing the mini-tub. You pick up the same 1/2" or so you gain when you do the 1/2" spring offset, and then you hit the inner tub.
On my Duster with a 1/2" spring offset from DoctorDiff the inner tub is the limiting factor. Before I added my rear sway bar I would occasionally get a tire to rub on the inner wheel tub when I was going over a speed bump or big driveway transition where you get a significant cross-axle kind of action.
