['ol Pinion head]

Originally Posted by scott70

OPH...you spoke of the 12 bolts that came in the 455 A-bodies. My 70 455 gto still has its original 3.31 posi 12 bolt. What are the differences between that and the chevy 12 bolt? What parts will interchange? Thanks

On the 12 bolt c-clip axles that found their way under the '70-72 455 GTO's & '71-72 455 LeMans, they were all built of the McKinnon plant in Canada. There was also some usage of this style rear in '68 & 69 Olds A-body's & '69-70 Buick Skylarks. These specific 12 bolts had different axles, backing plates, different drums, and a 3R pinion yoke. All different than the common Chevrolet application 12 bolt rear.

The McKinnon cast 12 bolt housing will also not have a date code cast into the lower pass side webbing. Instead, the housing is date coded on the front of the lower "lip" area of the housing, visible from the front of the housing. On many McKinnon 12 bolts this date casting may not even be legible, the casting date is quite small.

McKinnon (GM of Canada division) also built some 12 bolt "Chevelle" rears for Chevy usage, I've ran across several out of '69 & '70 "Chevelles". These will have the Chevy specific ID codes, as well as the standard duty Chevelle ('70 F-body) length axles, smoothie style drums, & the very common style "Chevy" backing plates with the spotwelded flange.