8 3/4 rear axle coding?

There is no stamp or part number on the housing itself, and as you know, the part number is cast into the center section housing. There are 2 different A body housings, a pre 1970 and a 70 and later. You can easily tell them apart by looking at the location of the brake line splitter block. The pre-70 unit will have the splitter almost on the center hump, while the 70 and later will have it down on the drivers side tube a few inches from the hump. Other than that, you may find some inspection marks on the rear of the housing written in crayon, and maybe some colored paint daubs on the nose of the center, indicating gear size, SG unit, and pinion nut torque. Those can be found mostly on HP cars and B bodies, but it is possible that some show up on HP applications of A bodies as well!