The blocks should work for the back, but I'd be wary of axle wrap. Personally, I'd find a rear end out if a newer van, with a lower axle ratio (4:11??), swap the spring perches and shock mounts.. the van axle is about 4" wider flange-to-flange. While you're at it, disassemble your leaf pack, slip 2-3 extra leaves in it and bolt it back up.
Put 4 leaves in my '90 Suburban when I swapped the axle with an 8-bolt out of a 1-ton van, gained almost 7" of lift, AND turned my 1/2 ton into a Ton Plus, carried 2500lbs of sheetrock w/o bottoming out.
Added 3 leaves to my current Tahoe, got 3", and a much more stable ride going thru corners, truck doesn't sway at all.