Without getting into the rear end, with all that Honda goodness and design, if there was a way to mount one rear wheel on a bearing plate or clutch, it would make it a lot easier. Maybe something between the current wheel hub and wheel?
I like to borrow components that already exist as opposed to making my own when possible, so I am thinking of a front spindle assembly from a car that accepts the current wheel flange on one face and the wheel on the other.
Find some cheap, common, spindle maybe, even a trailer hub with mounting plate, drill, bolt, maybe scab a plate to accept the current pattern, and in my dream, use one with the same bolt pattern as existing wheel for the outboard end.
The kiss of death with this type of cobbling is to select something off a 1963 rambler cause you found one in your shed, you doom the project because when it fails, you end up hunting parts for your new orphan.
Tie Down Engineering 5-Lug Hub/Spindle End Unit for Build Your Own Trailer Axle System 1750-Lb. Capacity Per Hub, Model# 80117 | Northern Tool + Equipment
One side would be wider, and it may damage something if you went airborne, try it and let us know!