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.
Your going to need to pull an axle to know for sure. By the time 1970- rolled around they were into the OILED bearings Set9 mid size car and Set10 full size
My Timkin book says 1970 Riv was set10 and 2689S seal (Oiled Bearings) The Electra, Wildcat, Lesabre and Estate wagon were still old sealed bearing in 1970 Rivs usually always got the best newest technology...They were like the corvette of Buick personal luxury. Jim
