Ahh, but in the craziest turn of events, this motor has a 2658920 head on the drivers side, and a 2465315 head on the passenger side, although neither head looks to have ever been off!! Hmm!!!.....
2465315= 64-65 273 head
2658920= 67 273 head
But the craziest part is that the block casting is 2806030, which decodes as a 67-74 318, but is clearly stamped B273 4-12 and the casting date is 3-3-66!!
Late casting?? Mutt motor leftover parts?? I'm now stumped!!!...