The stage 1A head was thicker, had bigger ports, and could take a bigger valve, they also had stud mounted rockers like a chevy.
There were about 50 sets made I have only seen 4 sets ever and 3 were in one place. I bought a set which I sold to Terry Houston who, I believe, sold them to Red. If I could could find another set I would get them in a minute.
Mike Licht