[Twisted78SS]

I guess I was a bit surprised when you asked if it was rare, in reality, from late 71 or early 72 on, half ton 2wd trucks made the switch from 6 to 5 lug axles in the 12 bolts (among other axle styles, Dana, Eaton etc...) so they are everywhere.. They are a bit different than a car 12 bolt, I believe the car actually had a bit larger pinion shaft diameter. The ring and pinion are not interchangeable between cars and trucks either. The vast majority seem to be open carriers, and gears came in quite a wide range. For a posi, the Eaton limited slips were the one's I've seen the most.