I dug the 48 out and cc’d it. Been in storage awhile, a little different than I remember it. It wasn’t beed blasted like I remember and I thought it was a bare head. Lol. So I am not batting 100% on what I remember. But I cc’d it again at 71-72.
The date code is f179. Very late 69 head. I also notice a X stamped on the head above the 4 on a head boss. Probably means something, just not to me.
. Could be a machining or set up designation. I.E. similar to what Steve25 mentioned.