So you have 4" block on top of the stock 2" block? To sit at the same level you'll need shackles 12" over stock length, which should be 16" long.



I ran 12" shackles with the stock block on my 88 for 4" of lift. It rode pretty wierd. The leafs were prettymuch flat, and I wouldn't be surprised if yours were inverse (mine were when flexed). It messed with my pinion angle, and Im on my 3rd driveshaft because the ears on the previous 2 were too hammered to remove/install a new joint, or the ears broke.
It will ride pretty soft, but will flex like freakin crazy. You could get some pinion shims to correct the angle if you wanted, I never did. I don't know of any shackles that are sold, but if you make some, make damn sure they have A LOT of bracing, the twisting force on those things is gonna be ridiculous. Also if you carry a load, the rear end is going to squat very low, further messing with your pinion angle. I did it once and toasted the rear u-joint in about 15 mi.
I now have Belltech 6400's and I weaved an extra leaf in my stock pack... It sits maybe 1/2-1" lower than I'd like in the rear, but its about level, and rides good so Im content.
I personally would go for the belltechs and maybe an add a leaf, and keep the stock block. If you want to ditch that also, I'd maybe throw the AAL in a set of Exploder springs and see where that puts ya.