I just picked up a 12 bolt rear this past w/e for my 68: the seller said it was an original 68 rear. For the price negotiated, I grabbed it without verifying any numbers.

Where are they located, and once found, how to decipher them to determine build date and original ratio?

Thanks!

Front of axle tube on pass side, mid distance from spring perch and third member. Clean and lightly sand. Should be two letters the maybe 4 numbers then letter and maybe another letter just below. Ie : BU 1123 G
E

Actually my stampings.

http://www.camaros.org/drivetrain.shtml#RearAxleNumbers