compression ratio on pump gas

Hey Jack thanks for the info. I also am at sea level and i can still take the XE262 out if it will help,But where dose that leave the valve guide to retainer at or do i need machining done to the head. With the XE262 and 1.6 rockers lift is already at just over 500". I was told to keep it close to that to be safe. Can the stock Magnum head take XE268 with no machining. What do you think????