['ol Pinion head]

It's really not a mess, its actually easy to understand, if you look at it as a continuation of improvements as power levels rose as the torque loads increased with more powerful engines. Through the 60's GM had 4 divisions building A-bodys in the US, & each division basically had its own gear & axle assembly at least enough autonomy that in '68, 69, & 70 each division had its own rears. GM, Ford, Chysler all increased the strength of their rearends in their highest performance vehicles as the decade rolled on. Warranty claims is not what they wanted, so they upgraded... at least behind their performance engines.

In GM's case, the common Chevy 12 bolt was not the General's strongest factory A-body or F-body rear. Not unless you happened to to have been one of the very few who ordered a COPO Chevelle, an L78 or LS6 Chevelle, or COPO Camaro, or an over the GM counter version of one the truly HD 12 bolts for those cars. The rest of Chevrolet Divisions Chevy 12 bolt offerings, the vast majority of Chevy 12 bolts built had weak axles coupled with their really weak link: the brittle spider gear/side gear combination. Truth be known, the 30 spline standard duty Chevelle 12 bolt axles lack a lot in strength to the best bolt-in 10 bolt axles, thus counting axle splines really won't tell the whole story. In the case of factory Pontiac 8.2 axles, it wont tell if a 28 spline sealed bearing axle is a regular light standard axle or if is is one out of HD SAFE-T-TRACK rear. As far as metallurgy of the 12 bolt Chevy center housings I have not studied that a ton. Would love to compare a 69 BE coded Camaro 12 bolt to the '69 BV I have in my racks. Both are 4.10 positraction Camaro units, the BE has all the good stuff & has a different casting number on the hsg. Nodular iron, a good bet.

More on axles... the bolt in axles out of '64 or 65 Olds Cutlass or 442 or Buick Skylark or '65 GS will bolt right in a '64 or '65 Pontiac 8.2 rear, and are the same strength std duty axle. Now what about the fellow who just bought a early GTO or LeMans project car & over the previous years, the Pontiac's original rear was swapped with the weak early Buick 8.2 out a '64-66 Cutlass or '64-66 Buick Skylark. They look nearly identical, but the strength of the gray iron center section early Buick 8.2 is not near as strong as the "weak" gray iron Pontiac 8.2 housing out a '65 Tempest, LeMans or GTO. Olds even specified the Pontiac 8.2 in many of its higher torque application '66 442's. that housing was just Pontiac's standard '66 gray iron 8.2 housing rear. Not the nodular 8.2 Pontiac housings which first started showing up in '67 Pontiac A-body 3.55 Safe-T-Track applications. The nodular hsg 8.2 was really needed behind really strong applications like the '66 L79 W30 442. Olds instead dropped the 8.2 & developed the type "O" 10 bolt rear which lasted a few years.