Well, I've found that using 2" lowering blocks on the rear of my truck has left no driveshaft play at all. When going to remove the driveshaft where it meets up to the rear axle, it's hard to get the driveshaft to disconnect after you've taken the 4 bolts lose that secure it to the rear axle. Should not have to do much to get that lose and have the rear driveshaft drop and be free from the rear axle. What happens in turn with the no play in driveshaft is that it puts tension on the transmission going forward toward the front of the truck. Recently, I had my transmission go out on my truck and my dad and I couldn't get the transmission to disconnect after taking all the bolts out that connect it to the engine! We ended up having to cut the front input shaft because it flared around the edges and wouldn't come through the pilot bearing smoothly like it regularly should. So, I'd much rather use drop leaf springs now to see if I can gain the factory play in the driveshaft to make my current transmission last much longer than the last one.
http://www.zmotive.com has 3" drop leaf springs for an 88-95 Isuzu pickup and I'm not sure if that will fit onto the older 81-87 Isuzu pickups? Plus, I'd rather buy a pair of 2" drop leaf springs as I don't want to drop 3" in the rear. They also sell 2" drop leaf springs for an 84-88 Toyota pickup and I'm wondering if I could buy them and have them work on my 1982 LUV? As long as the measurements are the same I don't see why not.