Its funny, I have been trying to clean of the shelves by putting some heavy items in my Ebay store. That is why I came across these heads. When posting them in my store I did a Ebay search for the casting number and found a similar set with the same type of date:
http://www.ebay.com/itm/Chevy-Camel-...-/110901953826
I wonder what the Y is?
Jason