I found a nice Drum to Drum Posi Diff.....but......It's a Pontiac 3:55 posi diff out of a 66 GTO. The guy changed the spring bases to be correct for a 67-72 A body, and had it in his 67 Lemans. It's actually maybe only 1/4" narrower than the 12 bolt "O" in my brothers 70 Cutlass right now. It "should" bolt right in, but my 1st concern is the yoke is different. The one on the Pontiac is a 27 spline. Anybody know off hand what it is on the 12 bolt and if they are interchangable? This started in another thread, but the topic has evolved..
Thanks for any input,..

 

If your rear is a 12 bolt OLDS (bolt in axle rear with 12 bolt smooth rear cover the u-joints are the same 1 1/8" cups same u-bolts everything.

IF you have a 12 bolt CHEVY rear end c-clip retention 12 bolt cover with a upper eyebrow bend in the cover it will have a 1310 or 1330 yoke with U-bolt or 4 bolts and 2 straps.

NOW if you have a 12 bolt chevy rear and your car is original Canadian car it will have the same 1 1/8" cup yoke with same u-bolts too.

ALL the BOP yokes will look the same and have the same yoke u-bolts from 1964-1970 Pontiac all the way to 1972.

Pictures from left to right-
Pontiac 8.2 and 12 bolt olds (12 bolt cover 10 bolt ring gear) (27 spline) 1 1/8" cup
12 bolt chevy canadian BOP yoke (30 spline) 1 1/8" cup
12 bolt chevy 1310 strap and bolt (30 spline) 1 1/16" cup
12 bolt chevy 1310 u-bolts (30 spline) 1 1/16' cup