Question About J Heads

They are all the same castings. Ports and chambers are the same. Differences from 340 or 360 HP would be premium valves and valve springs. They also have Induction hardened exhaust seats. By the way , they are not "J" heads. "J" heads ran from about 71 to 72 on 340's and 360's. They still flow well and have the good ports.