Is there much difference between a van and a motorhome based on the same chassis?

My driver is a 74 b300 Tradesman, and a friend gave me a defunct 1980 dodge b300 derived RV. There's quite a few items that I think I could scavenge, but some, I'm not sure it'd work. For instance, I'm pretty sure the ~50gal plastic fuel tank will swap in for my stock metal, except for some questions regarding compatibility of my fuel gauge to it's sender (I have a potential workaround anyway), but what about the dually rear axle? Or the cruise control system?
I ask because the front wheels aren't the same bolt pattern, so I'd have to take the tires off the rims to swap em.
Engine's big block, so even though the tranny's the same, it isn't swappable, unless you gut it.
The headlight switch may or may not... the common Chrysler pull switch for the headlights has actually two variants-- a 7 blade or a 9 blade. This 9blade is the same switch plus an extra circuit for something, and a spot to dash ground. As far as I can tell, you might could use the 9 blade (which appears around the turn of the 80's, and was used into the 90's on Dakotas) as a 7 blade.
Haven't tried it, just seems to work from what wiring diagrams I could find.

Any thoughts or other scavenging ideas?