it is starting to look to me like there may have been more thasn one foundry making heads!
The head I just picked up looks very sandcast, the coring work is not as smooth as later heads, and the front bolt is on the fin level, the rib splits to allow this. Same as yours. I think it is the head made from #1026,147 through to #1064,902 that is the first head to use the bolt in the front.
I checked a 72 and 73 head and both had the bolt up higher in the rib.
I will add some info to the id heads thread.