['ol Pinion head]

Have personally pulled factory GM posi units out of over a thousand yard cars/ core rears, and out of own project cars, partscars/ loose customer rears that came in to be rebuilt.
There were a TON of rear axle plant factory installations of the alum posi tag where the embossed lettering was readable towards back of the car, then the tag was rolled over & when viewed one will see the back side of the alum tag, lettering is backwards! Often a coat of thin black paint or undercoat is on the backside of the alum tag from when car was originally dealer prepped. Near the build bench have big ziplock full of such used tags.