I just went to a custom engine builder to shop a [340/pre 72 360] core to start on (no luck), he warned me to stay away from flat tappet cam setups. Apparently the current oil formualtions are causing havoc with flat tappet wear. Even with additives apparently this is becoming a big problem.
I'm looking at a full roller setup now, I don't have a good reason to go over 6000 rpm.