all ss 396's had 12-bolts, but not all were posi's. (i know because unfortunately mine doesn't)
this was taken from the Camaro Research Group web site:
Q: [05-May-1999] New: What models received 12-bolt axles?
A: 12-bolt axles were installed on all SS-396s, all SS-350s (with possible 1969 exceptions noted below), all Z-28s, plus the other models itemized below.
Note: GM documentation indicates that early 1969 SS-350s and LM1s with automatic transmissions may have received a 10-bolt rear axle, with a 12-bolt axle optional. The extent of this is, as yet, not well known. Both 10-bolt and 12-bolt models seem to exist and CRG is still researching this. Please help clarify this by submitting your vehicle data.
In addition, 12-bolt axles were installed on the following cars:
L30/M20 cars from approximately Dec 1966 through the end of the 1968 model year.
All models with the 1969 factory 4-wheel disc brake JL8 option.
1969 cars with the LM1 engine. Use on the manual transmission cars appears certain. Use on the automatic transmission cars may have varied and may be subject to the same usage issues being researched for SS-350 in 1969 and described in the Note above.
To see a pic of my car, click here... pages.prodigy.net/mtbmtb/rf396ss.jpg
[This message has been edited by mike brown (edited 12-24-1999).]