I'm just wrapping up a driveline swap in mine. I used a rear from a 70's-early 80's Firebird. It is actually about .50" narrower than the stock rear. I seem to have been able to throw a pair of 225/75's on 15" junkyard steelies. I used the leaf springs from the donor Firebird. Don't know myself how much I can safely lower it though. Ignoring the bump-stop, with no spacers the axle sits about 6" from the frame rail. I have a long bed 1/2 ton and after all was said and done, I did require a 2-piece driveshaft. Be open to that option if you are considering lowering yours.