compression?

Well I recommend you have the machinist re-check. I've measured at least 5 sets of LA type heads in the last 2 yrs - 915s, 576, 596, 587 and stock were all in the 70-72cc range, and the 308s measured 72ccs as well. If you went with 78ccs for your calcs and they turned out to be 6cc less it would raise you compression ± 0.6. Up to you.