2wd Bike Tech had plans and kits, but went out of business before I could purchase.
Jeep Rubicon Classic Adult All Wheel Drive Mountain Bike.
1991 Legacy Ovation mountain bike.
I'd like to have a flexible shaft coupled to my Staton dual drive gearbox and drive the front wheel for off-road adventures.
Just ordered a spiral bevel set from Ebay. I'll either mount the large bevel gear to the spokes with a custom rag joint or make my own front axle adapter (like a sprocket adapter). Another possibility is to get a 135mm wide fork, a rear free wheel axle and mount the large bevel gear to a right hand thread disc brake adapter.
This is how BWA, Ovation and Christini, attach(ed) the bevel gears on the front wheel:
Wow this is the place to be for discovering new things. I can see some awesome builds which could be built with this technology. I really like the one which let you switch from single to two wheel drive.