['ol Pinion head]

The '65-70 Pontiac B series rearend is known as the "P series" 8 7/8" rearend. That is straight from the original manuals & also referred to in the Hollander Interchange manuals.

For a '65 Pontiac B series complete rear (or housing), one wants to source one from a '65-67 B series Pontiac.
Franks in CA is a good source, typically much cleaner appearance housings than ones sourced up North, the SE, or in the Midwest.
I do not stock this style GM rear. Over the years, have sourced, rebuilt several, & built several up with lower ratio gears for customers.
Have also reconfigured several later "MP" series low ratio (3.23-3.42) posi carriers to mate up in '65 & '66 Catalina rears.

Further GM B series rearend lineage...
For '71 GM models, there was a revision made to the "P series" 8 7/8 rear, this required a different spline pinion flange. This style GM rear's Eaton posi unit was also reconfigured for '71 models.

The only A-body's to ever receive an 8 7/8 P series rear were the '73-77's . C-clip axles were used in this body style specific rear.
From checking out multiple hundreds of these ugly wagons, very very few were equipped with posi units.

For the '77 model year another revision was made to the 8 7/8 P series R&P (a longer pinion).
This style 12 bolt B series rear is known as the MP (modified P series), or in some manuals, that model year's 8.75 rear.

The only GM divisional usage for the early '65-70 "P series" ring & pinion & 31 spline carriers other than in Pontiac B series vehickles was in '65 & some '66 Olds B series rears. Olds began to roll out their Type "O" Olds rears later in '66 B series. The Type "O" style 10 bolt rear was exclusive to Olds divisional usage in '67-70 Olds A & B body's. Pontiacs did not come with them. Olds guys love to call the Type "O" rears 12 bolts, but their smooth 12 bolt cover is the only thing "12 bolt' about them & even that 12 bolt cover has different bolt spacing than the common 12 bolt Chevy car rear cover.

Buicks...
Big Buicks of the '65-70 era never had their own version of the 8 7/8 P series rear. Buick instead relied on the 9 3/8 BUICK rear up through at least 69 or '70, Next, a revised Buick 9 3/8 (Salsbury/ non dropout 3rd member) style rear was used under '71+ Buick 455 powered Electra's & Rivieras. As the '71 model signaled the beginning of Corporate GM usage rears, certain engine specific models of '71 B series Buicks also received 8.5 rears as well as the afore mentioned '71+ 8 7/8 P series rear.
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