I worked in a Chevrolet foundry for 36 years, (starting in 1965, though). What you're looking at, I believe, on the casting number tag is the number "34709" with the imprint of a slotted head screw between the 34 and the 709. This was usually a shift marker to determine whether the engine was cast on first or second shift. If you look closely, you can see similar imprints from screws on either side of the daytag that says H 3 7
Hope this helps.
