What are these #'s on the frame?

[pritch]

I was taking a look at this chunk of frame from a parts donor that I kept for the automatic trans crossmember, and I noticed these numbers. No, they are not the VIN number. Are they like the part number? I got curious and checked my Panel and it has similar numbers in the same place. They are in the blue circle on the frame chunk, for reference.





The parts donor was a '68 C20 'Burb and that number is: 3935815-430 and under that is: 2-8-68-3

The one on the Panel, a '68 C10, is: 3935809-420 and under (really above-these are upside-down on the frame) is: 11-9- -2. I wonder if these lower #'s are a date, but they just didn't stamp the '68'?

Just wondering.