Lennox, Hello up in Canada! to answer your quetions the Pontiac 8.2 carrier and ring and pinion interchanges from '64-69. '70-72 Pontiac 8.2 10 bolt carriers and ring and pinions had larger ring gear bolt holes and 1/16" larger LH threaded ring gear bolts, and as a matched set can be used in earlier housings, or even combinations of later posi, older gears can be adapted.
Some history on the carriers used. The earliest Pontiac 8.2 Safe-T-Track carriers introduced for '64 Pontiac A bodies, all were 2 pinion cone type posi carriers. In good shape, these hold up fine in good shape in putt-a-round stock type cars with narrow stock type tires. For '66, the 4 pinion low ratio (3.36-5.57) STT carrier was introduced, as the 2 pinion 8.2 units weren't holding up well under higher torque load applications. The new 4 pinion STT cone type carrier was also avail as a service piece for warranty work on '65 models. Interestingly, Olds manual trans 442's received Pontiac 8.2 10 bolts. When ordered with low ratio gearing, the 442's recieved the 4 pinion STT units. Pontiac's 8.2 gray iron center hsg was cast with much more strength than the Buick 8.2 center housing, thus Olds needed it behind the early 400 Olds and a 4 spd.
Width... Pontiac increased the width of their division's Abody rearends for the '66 models, this same width stayed under Pontiac A body's and most GM Abodys through the '72 models. NOTE: A few of the very earliest usage '66 Pontiac A body rears have been documented to be of the narrower '64-65 width. Last, Chevrolet's Malibus/Chebelles/ Elco's all stuck with the narrower A body rearend through their '67 models.
Pontiac for '67, totally understanding the need for a stronger differential, esp with its stronger and stronger optional engines, and in an effort to reduce warranty claims, began casting its higher performance ratio 8.2 10 bolt housings out of nodular cast iron. Looking back, this was a bandaid in the overall picture, but any effort to reduce center hsg flex in the pinion area helps insure ring and pinion longevity. Have torn down dozens of blown up standard gray iron 8.2 rears that owners spent a lot of coin on hard to find at the time tight 4 pinion carriers, low ratio ring & pinions, and then blew the R&P to pieces at the strip in, for the most part, mid to low 13 sec automatic GTO's and early F85's. Picking up the pieces, and starting over, one eventually gets smarter.
More timeline history... Sometime between '67 and '68, the HD Safe-T-Track Pontiac 8.2 10 bolt rears were introduced. These included the nodular center hsg, the 4 pinion STT carrier and newly introduced HD forged axles. The HD Safe-T-Track 8.2 Pontiac in Pontiac A body's was only avail with 3.90's and 4.33 gearing. Have gone through the rebuilding of over a dozen HD STT's, not something one runs across very often.
By the '68 models, Pontiac became the only GM division using the Pontiac 8.2 10 bolt. Due to neccessity, Buick came out with their own strengthened BUICK 8.2 10 bolt for '68-70. Housing design, carrier design, ring and pinion design, axles spline pitch, all are different than the Pontiac 8.2 10 bolt. Note: the much strengthened BUICK 8.2 was used under the heavy and often very quick '70 Buick GS Stage 1's (stock 500ft lbs of torque)
Olds, also for '67, came out with their own rearend design, the Type "O" 8.4" 10 bolt. The Olds guys love to refer to them as 12 bolts, but only the smooth cover has 12 bolts, in actuality, the ring gear is an 8.4" diam 10 bolt. The type "O" Olds design was used through the '70 model year Cutlasses and 442's, and again only under Olds vehicles. Both the Buick and Olds designed rears are relatively strong in top condition, stronger than the previous gray iron 8.2 Buick and 8.2 Pontiac provided rears that were under the Buick and Olds A body's from '64-67. Desirable ratio ring and pinion sets and posi's are expensive for both, more so than parts for the Pontiac 8.2. I've rebuilt quite a few of each, and up till recently, for the BUICK version there were no aftermarket gear sets.
Like Pontiacs 8.2 10 bolt, both the Type "O" and the late BUICK 8.2 had rearend housing ends which were changed slightly for the '70 model, as GM went to tapered axle bearings in all their bolt in axle A body rears. This move coincided with the introduction of wider 70 series and 60 series tires beginning in '69 in OEM applications. GM's performance A body's and early Firebirds with sealed axle bearing rears were not designed for the increased side loading, thus the move to much more positive axle retention with a splash lubricated tapered axle bearing and external seal. The great thing about tapered axle bearings, they don't seize and chew up the axle mating surface like the preceding sealed style axle bearings.
1970... new decade, some would say the pinnacle year of the first Musclecar Era... for '70 model Pontiac GTO's built with the 455 engine, Pontiac engineers gave up on the 8.2 Pontiac 10 bolt rear and specified a McKinnon built 12 bolt rear, complete with slightly stronger cc-clip axles and a larger 3R joint flange than was used on standard usage Malibu/Chevelle 12 bolts. The major weak spot... the Eaton posi units used in the 455 application 12 bolts is they still had the same brittle spider gears and side gears as was used in nearly every oem application chevy 12 bolt Eaton Posi. Unless the rear is going back in a Putt-A-Round car, in a build, I prefer to always replace the side gears and spiders in these factory Eaton 12 bolt carriers. Have ran across too many high 12 sec cars that have shattered the small brittle spider gears.
Buick and Olds for '71 models introduced the 8.5 A body rearend under their A body product lines. Firebirds and Camaro's for '71 also received their own version, but with c-clip axles. Designed with a longer pinion and more pinion support in the center hsg than any previous GM A body differential, the '71-72 8.5 A body rear wasaver on three different housings, and was avail with two different size tapered axle bearing axles. In repetitive abuse on the street and strip, as a GM offered rearend, very hard to beat the 8.5 A body rear both in strength, availabilty of parts, and in total cost to build. Interstingly, the same strength stock axles that found themselves behind a 6cyl Skylark were also run behind '71 Stage1 and W30 models. Buick and Olds joint effort didn't cheap out on the metalurgy of the axles.
The only knock on the first 8.5's (71's) I've ever had is all of the factory '71 usage posi units I've ever examined were sourced from Warner Motive
Just another cone type posi unit that eventually wears out and is not as easily rebuilt as a clutch type posi unit. For street/strip use, I always replace the decades old 8.5 Warner Motive units with a new HD Eaton carrier. With the '72 models, the clutch type S spring corporate 8.5 Posi units began being used. This style was used up through the '70's then sparingly in the early '80's when GM was cranking out weak engine cars, then finally the 8.5's were used up through '87 in the Buick Grand Nationals.
In building performance A body rearends off the tapered bearing bolt-in axle 8.5 A body housing and properly rebuilt 8.5 s spring posi, it's been very common to have friends and customers consistently running stock A9 and A10 axle bearing 8.5 A body rears in 3600-3800 lb A body's down into the mid 11's on slicks. With GM discontinuing the posi clutches for the 8.5 S spring carriers nearly a dozen years ago, more and more I began building HD 8.5 A body and F body rears with Eatons 30 spline carrier combined with new Moser axles.
Hope this helps on a rundown of GM A body rears, need more detailed info, feel free and ask.