Is this a Mopar sure grip rear end?

The pix are kinda small, but from here, it looks like GM however NOT Chrvrolet. It would be Buick, Oldsmobile or Pontiac. Yes, they are different from Chevrolet, and there are few performance gear ratios available for the non Chevrolet 12 bolt rear........if in fact, that is what it is.
Do you have a picture of the cover? The Chev 12 bolt cover has an oil "notch" formed into it where the other GM 12 bolts do not. Those covers are smooth.

George