Well, any Ofna or HotBodies 1/8 diffs will fit for certain, as will the Jammin 1/8 diffs I think. The Ofnas are cheapest though, and quality is just fine by all accounts.
The FLM hybrids are really nice, though finish quality isnt all that amazing- a few rough edges and plenty of machining marks- do you like polishing?....
I personally use UE ultralite cases and HB 1/8 buggy diffs- solid, and beautiful too, and they fit inbetween any standard maxx type bulks.
The muggy diff conversion is rather cool, and they are most comparable to the UE option I reckon, if you get the alloy diff cases. As you wil have seen, it doesnt take much work to make them fit, but your gear ratios will be a little off, so you may need to adjust accordingly.