Was looking at some codes on the rear differential of my car today. I found a 7890 stamped on the back (towards the rear of the car) of the drivers side axle tube. I also found some numbers on the rear end housing on either side of the rear end cover. The number on the drivers side was C0N1 and the passenger side was K88. Any ideas about what these numbers mean? Thanks.

12345 67890 - foundry test marks

C0N1 = foundry control

K88 = foundry casting date code Nov. 8, 19?8

Is there any other numbers located on the rear end housing that I can use to figure out the original information on the rear end? If so where are they located?

The date and ratio codes were suppose to be stamped 8"-10" inboard of the brakes generally on the passenger side facing the front. These were hand stamped and sometimes not very deep. A wire brush and a strong light are usually needed to reveal it. It'd read something like CG1025B where CG would be a two letter prefix indicating the ratio and posi or not, 4-digits representing the month/day, and a letter designating the plant it was built.