I don't recall exact dates but I believe RAI was the only one initially available and was a D-port head casting #31. In May of 68, you could get the RAII which was the round port head. Forget the casting number on those...722? For some reason I think the RAII replaced the RAI, but not sure about that.

RaII IF IT WAS BUILT after may 20 RA 1 if built b4