I just put in a eaton locking differential in my car yesterday, the hardest part was getting the new bearing races in the housing, and finding the right torque specs for the pinion nut. all in all it took around 5 hours of working slow. If you get an eaton unit you have to get the matching ring and pinion for it or else it wont fit. I think the series 3 differential fits 373 and down, and the series 4 fits 410 and up.