Never saw a set of MACK 21 stud pump mount heads. I would be interested in seeing some info on those as well. Have you tried looking on GOOGLE for info on those?
A little larger picture may help some old eyes see this better
I once had a new set of aluminium pump in head, heads, one had FOG cast on it the other had ***. Nice clean castings with the American style combustion chambers. Canadian combustion chambers on these early heads are shaped differently. Brian
I have a pair of NOS heads that say FOG on one side and FOH on the other. I reasoned that the FO part was for FORD. The G and H had me stumped. When I pondered out loud on this, my wife suggested "gee" and "haw" like a dog sled musher would direct a team of dogs. Anybody have a better explanation?
Stan