"O" cylinder head casting

Does anyone have any info on the O casting small block head. I own a machine shop, and recently purchased a used set of these with 2.02 valves. I put them on a flow bench and compared them to a set of J heads. They were slightly better. The intake and exhaust ports are untouched and cc the exact as an X head. I am planning on rebuilding them to sell. Any ideas what these came on????