Where on a head is the part number

[Mercracer]

hhmmm, interesting... that was nice of them to stamp the clue on the outside for those anyway... is there anything usefull stamped on the outside of older heads?

Under the valve cover you can find 289 302 351 cast..... Nothing on the outside....

[1987cp]

Right, F3 heads (and probably F1 Cobra heads, been a while since I've seen one) say "GT" above the exhaust ports along with the three ridges on the ends, and F7s say "GTP" with four ridges. So happens the E7 heads I have, have a "T" in the same location. Is that universal?