I'm not aware of an airhead trike. I'm not sure it's a good candidate, although you'd think an axial drive coupling would connect to some sort of conventional back axle with a sealed bearing (conventional) prop shaft easily.
My personal view is that cutting up old airheads for bobbers and trikes is sad. An old, unloved or wrecked UJM being ideal. Power and acceleration on a heavy airhead trike might also be an embarrassment!
I saw a Yamaha XVS 1100 small trike with single saddle rider and WWII Stahlhelm helmet on the way to work. I smiled. Each to his own. I'd want more oomph and less outdated 'attitude'. Not the V8 and V12 monsters that were at Wainfleet last year, but a Hayabusa or something like that