You can put the Rear end from a 55 in to your AD truck. You will have to change the locating pins or the mounts on the rear end. I wont drill into springs for any reason so I would change the mounts to locate the rear end in to the correct location. That would mean some welding and careful measuring. Quite a bit of work for the same gear ratio. Look for an older SM-420 and take the parts off of it. Would be easier and cheaper I think.
