That is what I'm worried about, valves. Wondered if valve position in the modified J head would put the valve too close to a high compression block piston. Sounds like it should be ok, I need the open chamber I think.
I think you will be fine with both the piston clearing the combustion chamber and piston to valve clearance... Unless you have higher than stock compression...
Rule of thumb is if the engine has a cam with more than .500" lift, you need to check piston to valve clearance... However, I like to be safe and check it anyway to make sure...
I once over revved a 360 and floated a valve into the piston... Put the piston through the side of the block and bent the connecting rod like a pretzel.... I would rather check the piston to valve clearance to make sure it's ok, than to not check it and put a piston through the block instead...
