This is a difficult one to explain, but I'll take a stab at it..
882s are taller than 883s when they are sitting on the ground, but 882s in fact have a
lower spring rate than the 883s.
Cruiser Outfitters
Now, what LINY said about the 881s, 883s, and 882s being out of order is still correct. 882s do handle more weight than the 883s even though the 882s have a lighter spring rate. I know that doesn't sound right, but here's why it is...
The 883s are shorter, but since they have a higher spring rate, they don't compress as much as the 882s with the weight of the truck. In turn, the 882s compress more, but since they start out so much taller, their height still outweighs that extra compression and they still end up sitting a little bit higher than the 883s. If you add another 50 lbs. to the 882s, they sit right where the 883s are. That's why the 882s are rated for a little more weight even though they have a lower spring rate.
881s + top out spacers = ~3"
883s w/ 100 lbs. of additional weight = ~3" (that means that without that extra weight, the 883s will sit ~.5" taller than the 881s + top outs)
882s w/ 150 lbs. of additional weight = 3" (that means that without that additional 50 lbs., the 882s will sit ~.5" taller than the 883s and ~1" taller than the 881s + top outs).
Hope that clears up some of the 882/883 confusion.
Another note: No matter what coil you choose, the amount of droop is the same with OME shocks. That is because it's the shock's length that determines the amount of droop. If you stick a top out spacer on an OME shock, regardless of what coil you have, you will have more droop because now it's the length of the shock + the top out spacer.
The reason why it's not recommended that you put top outs on 882s and 883s is because they sit taller than 881s so you will be closer to full droop at rest which is harder on the CVs for normal everyday driving. If you are running
more than the additional recommended weight with 882s or 883s, then a top out spacer will be as safe as top outs with 881s.