1. The entire line of allison WTs are 6 speed capable, the clutch packs and planetaries necessary are all there, it's 3 reduction gears, direct, and double over.
2. The LCT series (aka 1k/2k) like previously mentioned are pretty much the same trans. The MH3000 is typically the trans used with a B in a motor home.
3. ISBs (pre common rail) have J1939 backbones and it would be pretty easy to hook a WT up to one (look at pretty much every school bus ever made with an ISB in it), the chrysler only can-bus common rails are a different story though...
4. You could do 4 wheel, but a divorced t-case would be a necessity.
5. I REALLY REALLY REALLY dislike working on RVs, as a matter of fact, I pretty much hate it. Ask any cummins tech what they dislike most about their job, it'll probably be the same answer. Most RV engineers must be on drugs the DEA doesn't even know about yet
-Will
allison warranty cert. / cummins tech