Great option without having to spend $$$ on springs, but that's still some coin. And work.
What do you want to do? Eliminate your blocks? Getting axlewrap now?
Do you want your rear springs to flex with the terrain off-road, or do you want more stability on-road?
I lifted my rear end about 2 1/2 - 3", disassembled the rear spring packs, and slipped extra leaves in between each of the 4 leaves. The three extra leaves I stuck in, I measured (and cut on a Metal chop saw) to be exactly 1/2 the length difference from one of the original leaves to the next.
All I had to do to bolt the extra leaves in was to enlarge the hole for the locating pin in each of the leaves to 1/2", then I used a grade 8 bolt (with the hex head rounded in a grinder) to bolt everything back together, and locate the axle.
My '90 Suburban 1500 I had, it was unfortunately a 2wd - I grenaded the rear end (twice), and decided I wanted to upgrade. I put an extra 4 leaves in that pack, and swapped in a 1-ton rear end from a '94 Chevy Van - it was 4" wider flange-to-flange, all I had to do was weld on new spring perches and shock mounts, and use a crossover 1/2 ton-to-1 ton U-joint. All told, I gained almost 6" of lift with it, so I had to use U-bolts to clamp the leaves together some - brought it down to 4", and it rode like a tank with the minimal flex, but I always had it loaded with tools, so I didn't care.
I've done this mod to my old '88 Blazer, the Suburban, and now my '96 Hoe. With all three, I immediately noticed a much more "sure" sense of sticking to the road, no swaying around turns... even when towing trailers (or the boat). I also increased the load capacity, the 1/2 ton Sub had well over 2300 lbs of sheetrock in it for one job, and never bottomed out.
