I pull this four wheel rough terrain flatbed trailer behind my 406. It weighs 2500lb, has a safe working load of 8000lbs and air/hydraulic brakes.
The HIAB 8108-2 was originally mounted on the rear of a HEMTT ten ton truck.
I like the hydraulic winch attachment. The crane lifts 5400lb at 16.5feet and 4500lb at 20.5feet.
According to my manual the crane (5000lbs) is too heavy for my mog.

Can someone tell me how large a crane a 406 can accomodate?
I am dreaming I can adapt it so it can be carried flat on the trailer and unloaded to an upright position with winch and/or hydraulics. The slide/tilt off the trailer would have to be done on flat ground.
I could mount behind the Unimog in a spider crane configuration. That is, add a 7 foot leg to the bottom support out the back and a leg to the Unimog sprag. Thus I would have 3 support legs and the Unimog sprag on the ground would make the remaining support.
When not in use the Unimog could be detached and the crane stand on 3 legs with the boom extended past the middle leg for balance.
Mobility would be compromised but this setup would be used for a few days at a time as part of a skyline operation in steep terrain.
Sounds a little crazy but I like salvage projects and I think this could be done for very little money.
Any suggestions or comments?