X Head cc's

My 68 340 X heads have been milled .020 and they CC'd at 70.68 cc's with O.E. valves. I'm replacing the valves with REV Ind. valves and believe Dogdart65 is right about the valve type making a difference although I haven't proved it yet. Hope to have the heads together by end of next week and I'll cc them again to see how much difference the valves make. Hopefully I'll gain a little compression with them.