I don't know, maybe it's just my way of thinking, but i don't think you can get too big of a head in a 23* design for a 406" motor. Look at the NASCAR guys running symetrical port heads flowing around 400 CFM with 358". Some 406" motors make over 900 HP with Buick 18* heads. I wish i would have built an 18* motor instead of a 23* head 434" motor because of the limited flow rate of 23* heads. I've got an old set of Brodix 10's and they only flow 314 CFM with 2.140 int. valves fully hand ported and flowed.
JMO
Zip.