To summarize: Model years 66 to 70, all SS Chevelles were sold with a 12 bolt. Posi-Traction was optional. 71-72, since there were SS small blocks available, 10 bolt rears were a definite possibility. Big-block cars should still be 12 bolts. Any for real 68 SS 396 should have come through with a 12 bolt.
On a related note, if you are trying to verify a real SS, look for the SS frame brackets that connect the frame from the forward lower control arm bushing location to the corresponding forward upper control arm bolt location. I wouldn't think a 10 bolt car would have these from the factory.
If you go to the Resto Shop on the Home Page for Team Chevelle and click on the 68+ section of How to Identify a Real SS you will find that the cowl tag on a 68 will tell the story.
Hope this helps Tom....
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