It’s a 489 with a cone type SG ( Not a posi, I didn’t machine it to fit the GM carrier in it). It appears the pinion has rubbed the carrier at some point in its life.
there are 3 different casting numbers mopar used for their 8 3/4 chunks, each with a different size pinion shaft, 489 is said to be the strongest of the three)
there are 2 types of sure grip units, the cone style and the clutch style (clutch style being more desirable because it is rebuild-able where a cone style technically is not)
posi, is a chevy term for their version of a limited slip differential which would not fit in a 8 3/4 rear axle and a pet peeve of many mopar guys
(just like i cant stand it when people call a lugnut wrench a tire iron)
the rubbing on the carrier is something ill let the OP expound upon