Were the rears stamped with a gang stamp like the blocks?
Not an expert in any way on these, but could that have been a BL (CBL?) rear at one time ? The top of the "E" looks higher than the B, suggesting a bigger font on the E than the B as the bottoms line up ?
1970 Nova's got CBL coded 12 bolts, with a 3.07 gear, but they were not Posi.
From what I see at CRG, 1968 Camaros could get a BE rear, but they were 12 bolt 2.56 rears? Wow.... That would have gotten me excited if I peeked under a 68 and saw a "BE" rear 12 bolt!
http://www.camaros.org/drivetrain.shtml#AxleCodes
Just thinking out loud. Seems like a smoking deal if it were real, and it seems to still be there, so......
Rich