I bought a 340 yesterday and guy said it came with a set of J heads and when I got it home and cleaned up I noticed it had one X and one J head. I know there is a difference in valve size and springs. but do they have the same size chambers inside? Because im going the have the valves and springs replaced anyways I was wondering if I had the valves upsized to 202 160 like the X would they be the same or would I need to find another X