I have a set on my SBC in my truck. Made from 1973-80 only. Only sold at dealers as after market. Used by Grumpy Jenkiins, on some of his legendary SBC'S. Your above info you posted is correct, also 180 cc intake runners, hard to find these heads, no heat riser provision also. Used by dirt trackers in this area, for class rules. Thick castings, mine had hardened seats, cast intake valve, stainless exhaust. My opinion, the best old school heads. Hope this help's, Ken.