['ol Pinion head]

"Corporate 8.5" is just a later day description for all the 8.5 differential, not nearly as bad as the foolhardy connotation of a "BOP" 8.2 10 bolt.

GM divisions had a lot of autonomy in differential mfg up into the early 70's when more divisions began to share more specific rear ends. It wasn't that way in the '60's, just compare the rear suspension designs & rear ends under each divisions big cars.

The 8.5 rear design was introduced for 71 model GM passenger cars. GM 1/2 ton pickups would have to wait til '77 model year.

1971 GM 8.5 uses:
A-body: Buick & Olds both mfg 8.5 bolt in tapered bearing axle rears for the A-body.
Little over a million were installed in two production years.

B body:
for '71, most GM divisions used a c-clip axle 8.5 B series rear in their base B series models.
LeSabres, Impallas, Catalina's w 400 engines.
Most likely Olds 88's with 350 Olds engines, can't remember stripping a '71 Delta 88 rear.

F-body, c-clip axle, often when equipped with a posi unit, that posi unit was a Warner Motive cone type posi (think a light duty Auburn style carrier).

1972:
first 8.5 X-body was installed.
'71 Novas & Ventura II' s originally had Chevy 8.2 10 bolts

Cadillac did not use an 8.5 rear till the introduction of the Seville in mid 1975.
These were nothing more than a Nova (X body rear). For '77 model year, the Seville gained rear disc brakes w 5 on 5 bolt pattern axles & rotors. The calipers & caliper brackets for '77 & early '78 model Sevilles was one style, late '78 &'79 are another. In the 90's & early 00's I stripped many dozen Sevilles of rear disc pieces as well as stripped down quire a few to bare housings, occasionally with a #9 (high ratio) posi carrier.