Weird 12-bolt - need help

[Kraska]

I purchased a 12 bolt differential from a 1970 Cutlass (supposedly). When I
say 12 bolt, I mean there were 12 bolts holding the cover on. I took it home
and disassembled it. Much to my surprise, the ring gear was 8.5 inches in
diameter (at it's widest point) and attached to the carrier with 10 bolts.
It didn't look like the rear end had ever been disassembled before.
I purchased this rear end to eventually go in my 55 Chevy Bel Air ( it's
about 1 inch wider than my old axle. I didn't care much about gear ratios
because I plan to buy a new posi carrier and new gear set.
What do I have here? Ever hear of a 10-bolt gear set in a 12 bolt
differential? I have a book that says the ring gear diameter for a '70 12
bolt should be 8.875 diameter with 12 bolts mounting it to the carrier. The
book says 10 or 12 bolt refers to the number of bolts attaching the ring
gear to the differential and that it is just coincidence that the number of
bolts attaching the rear cover is the same (Chevy by the Numbers - Alan
Colvin author).
Would it be possible to buy a 12 bolt carrier and gear set and put it in
this axle? Here are some specs on this differential:

Pinion:
stamping: 16A41_GM AT
394700 151
27 splines
max diameter of splines - 1.168
overall length - around 8 5/16
diameter of front bearing surface (closest to splines) - 1.1875
diameter of rear bearing surface (closest to gear) - 1.627

Ring Gear:
stamping: 16A41 GM DH 153
diameter at largest point - 8.5

Carrier:
casting numbers: 356 GC
there is a cast screw plate number of 124
diameter of outer carrier bearings - 2.8935
width of outer carrier bearing - 0.6465
overall width of carrier from outer edge of bearing to outer edge of
bearing - 7 13/16

Axles:
28 splines
max diameter of splines 1.196
outer axle bearings are pressed on axle.
axle is retained by bolt on plate at brake backing plate (no C clips)

Differential housing:
casting numbers 402227
other casting codes: CFD (or GFD) B (or 8) AB

Given the info I have provided, would I be able to buy a 12 bolt posi
carrier and gear set and install them in this differential? Would a 12 bolt
pinion fit? Is there a difference between a 10 and 12 bolt pinion? Would
that make sense, or should I just take it back and try to trade it for a 10
bolt from a Camero? (I should of gotten a 10 bolt Camero in the first place,
but no, I had to have a 12 bolt!)
By the way, this differential will go into a 55 Bel Air with a modest 350 V8
with a 700R4. Mostly daily driver with the occasional exhibitions of speed
as required. (Please don't lecture me, I know I don't "need" a 12 bolt posi
for a setup like this :) )
Any help would be greatly appreciated. Thanks.
Jim

[Ken Kelly]

Hot Rod or Car Craft did an article on building 10 Bolt rears recently. They had
a section on how to identify the different 10 Bolt rears. I remember a warning
about some BOP 10 Bolts having a 12 bolt cover.

Ken

[mrvette]

What you have is a unique Olds dedicated rear ususlly found in cutlass
stationwagons...usually non-posi....it is a bigger unit than a 10 bolt 8.5
rear, heavier axels...with two diferant casings available...
This unit is useful only to an Olds restorer....limited usage....

I'd get it back to where it came from, and just get a posi with desired ratio 10
bolt and have done with it......323 to 373 is nice for the street....
Parts are hard to get, and no great amount of aftermarket gears exist...not
anymore...hard to get 10 years ago....now? impossible..

GENE