Question about OEM frame number stamping

[Clatterville trolley]

I have a frame that I purchased and was trying to identify what year it may have been originally. There are numbers stamped into the side of the rails that appear to be a part number, either GM or supplier that stamped out the frame rails for GM. However, under the part number I found what appeared to be a date 10 6 79 - frame looks for all the world like a 67-72 frame, but if that is a date code it wouldn't be a 67-72.
On top of the frame rail just behind where the steering box bolts in is another number with about 6 or 7 digits and one letter - is that the serial number / vin number?? Is that number keyed to vin on truck cab from factory?

Any thoughts, suggestions, ideas on who to check with?? Thanks in advance. Jay