Re: 1970 camaro 3.73 12 bolt
 

In regard to the COZ stamping...... after further investigation it appears to have been available with a Turbo 400 as well as a 4 speed in 1970 but still Z28 only. According to what I read in Chevy by the #s the 3:73 posi gear set (COZ) was only available on the 350 Z28 in 1970 and no other Camaro or any other car in the Chevy line. Here's a link to the rear end and gear info posted over at Nasty Z28, a very informative site particularly if you have a second gen Camaro

http://www.nastyz28.com/camaro/camaro70.html#axle

So Gary, in answer to your original question, the rear end that you have came out of a 1970 Z28 buy it could have been an automatic, or a 4 speed.