I've got a 1970 Riviera GS. I have what I was told is the original rear end for it. I can't verify because gramps isn't with us anymore. The carrier is punched with 1383525....41-12 .... GMC. I think that makes it a 3.42 posi unit (its definitely a posi, kind of hard to mistake after the cover is off). The housing is stamped 1232649 and 261 and CFD and P PY and (an incomplete) N 268 (could be 263). 30 spline, bolt-in axles. I tore into this rear end aiming to swap it back into the Riv. I managed to source all of the bearings and rebuilt the center section to my satisfaction. BUT! I can't figure out what axle bearings to use. I ordered Timkin SET10, and they're way too small. The bearings that came off are closer to 3 1/4 inch outer, 1 1/2 inch inner and roughly 7/8 inch thick. I can't find a part number for them anywhere. It is entirely possible I'm overlooking something obvious. I've been accused of being a little slow some days. There's a completely different setup in the car now, I was told it is a 2.65 open diff and that seems about right to me. The diff on my bench looks identical to the diff in the car.