'71 318 compression...

My 68-7x whatever 318 heads CC'd at 69cc, look around, everybody will tell you that the Mopar heads have larger than advertised chambers. I went with heads advertised at 57cc and they were actually 63cc AFTER .015 milling.

There's absolutely no reason to use big valve/port heads unless you're going to tear it down and go with higher comp pistons. There's no other way to get good comp on a 318. With the new heads and thinner gaskets (.029 if I remember correctly) I'm lucky to be at 8.6:1. I'm running an xe268 cam from Comp. I think anything more than that is really going to need more compression and pistons are the only way to get it.