Class C Construction Hackery

Unless it is a molded fiberglass house on the back I think you are not going to have any luck removing it as one unit. They are built up in place on the truck chassis and in that era most of them have a lot of wood framework in them. They rely on the truck chassis for their rigidity. IF you could get the floor unbolted from the truck chassis, you would likely be trying to lift a wet noodle off the back. The only way I could see doing it is move the whole thing to the final resting place, separate the house from the truck, lift the house and pull the truck out from underneath. Personally I think fabricating a purpose built chicken coop is a better idea and less work.