HRL;
Two speed axles work with a planetary gear set with a sliding "clutch" gear. So there are different set of circumstances vs. a synchromesh/cluster gear set up in a transmission.
I'm thinking that your idea of shifting will probably work. We all know that you can shift without a clutch if you match the RPMs, reduce torque, etc. The thing that I don't know about is running the helical cut cluster gear backwards with a vehicle load.
You are correct about the VW/Corvair setup but that gearset is a hypoid design and the GVW is/was a lot less than an RV.
I think your idea will work in theory but my only concern is the longevity when the unit is in "redneck overdrive" under load for long periods of time. You should make your conversion "bolt in", keep the original driveshaft and "GIT-R-DONE"! It may work just fine.
SimS
