X-heads vs J-heads: what's the difference??

OldmanRick said

I think so too. I really thought the 66/68cc range was more the norm on X's? But, like I said earlier, you really have to check to be sure.

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If the valves were receding, wouldn't that give you a larger CC? Maybe it is time for a valve job. If so, I would have installed harden seats on the exhaust. Not sure 100%,but I believe the "J" heads were a 360 head, used on the early 360 2bbl. Some were machine for the 70' 340 6-pac., with angel push rods. I don't recall any were used on the 340 4bbl (X,O and U, were a 340 head).