http://www.ebay.com/itm/1969-Camaro-COPO-BE-code-12-Bolt-Differential-Complete-Ready-to-Bolt-IN-3894860-/191846230084?hash=item2caaed2844:g:9Z4AAOSwZ8ZXAapN&vxp=mtr
That looks like a good stamp, I have another close date of 0317, and 0305, and 0306. Not so sure any of the posi is OE, you can't tell from the one photo, except the springs are not right.
Mike
What I found interesting is the person with the rearend also has the cowl section from "the car" but unfortunately doesn't have the hole for The ZL2 option..... Hmmmm
Find out if the internals are COPO. Those are the important parts.