Pork: I just completed replacing the ring & pinion on my front 1/2 ton differential (it is the same as the rear). I can check the casting numbers on them tonight. On mine, there was one punch mark on one cap with a corresponding punch mark on one carrier side. The other cap had two punch marks & the corresponding punch marks on the other carrier side. I used that to maintain their relationship. However, I don't remember if the punch marks were originally there, or if I put them in prior to disassembly, you might check that. In any case I'll check my casting numbers for you tonight.