I replaced the crashbox on my 46 1 Ton with an SM 420. I had to get another bell housing so the pedals have something to bolt onto. This may not be an issue with the AD's or possibly your year. I had to make sure the starter gears were the same as the flywheel teeth, the clutch lined up fairly well and works fine, and I had the intermediate drive shaft shortened. It was not that hard to do. It is worth the work.
