I was not able to find any markings concerning the date of manufacture, Gray base, blue cylinder covers, ceramic bead insulation on the wires.
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I had not found anything either. I basically had the same engine you do. The seller had it since new. Boy was it a week long cleaning and putting back together.
I haven't started cleaning yet, Mainly just testing the mechanical bits as I go.
Tonight I put new balls and washers in the pump sections and ran the engine on air.
It seems to work but I noticed afterwords that I didn't have the lubricator cap on.
https://youtu.be/N-OmtVZmiwY
I forgot how hard it is to film and hold the airline at the same time.

Bill
Great project, Bill. Please keep us informed as you make progress.
Well, you must have done something right, it's pumping water

and it looks good with the new washers