I have a set of heads on my car with the casting number 3991492. They also have an "x" cast into the space between the end intake and exhaust spring pockets in line with the head bolt hole. I've been told that the "x" is foundry mark. Can anyone confirm that or have info on this version of the 492 casting?
TIA
I don't think they are anything special. On SOME cast parts they used an X on early test type castings, but then on some heads like the 487X it does mean something. I used to always look for the 487X castings, bought several sets and so far haven't used them.