transfer case trouble

[docrock]

I have a 72 Chevy Truck with the running gear out of a 81 suburban. Recently I was driving and the rear wheels locked up. I put the truck in neutral and got it towed to my garage. my mechanic took the case out took it to his shop, and he said it was not rebuildable. I found a low mile case and installed it and the truck does not drive. I switched gears in the transfer case and still nothing. I have a terrible noise from the trans putting it in park. I pulled the transfer case started the engine put it in gear and the tail shaft spins. I did not grab a hold of the shaft to see how much torque it was putting out or if it was just spinning. With the transfer case on the ground I put it in gear and it seems to operate properly. while it was in 4 high I reinstalled the case and the same thing is happening. It wont drive and it wont go into Park without making noise like Im trying to be rolling and put it in park. Please help