I don't know how relevant this post is but here goes... I just replaced the front springs on my '91 Sub which has a 2-2.5" lift. The front springs had eight (8)! leaves and they were going into a negative arch and you could see light through them, they were shot. The truck rode like sh#@! My friends' '91 with a 6" Superlift only had 5 leaves up front and rides like a dream. I ordered up a set of Superlift Softride springs and they came with 4 leaves only. Plus they are tapered on the ends and the other ones were not. Bottom line--HUGE improvement! These new springs are just barely positive arch, almost flat.
I also replaced all my ball joints and tie rod ends at the same time because my steering was awful. The ball joints (all non-greasable) were frozen up. It's like a new truck now.
I'm just using blocks in the back, I'm not sure what length they are. After a dozen Michigan winters, we didn't feel like trying to remove the shacle bolts which are probably naturally welded (rusted) to the frame
