Is this what I think it might be?

That's an X. Is that what you thought?

Yep, that's what I thought. :D
I was wondering if it could be an X head, but castings show 68-74 318 with 60cc chambers.
Just curiosity more than anything.

I was also kinda wondering why it's there on one head and not the other when they both have the same casting number.

Smart A's :D