Use 1.6 rockers. The P heads peak out their flow at .400" lift and only flow a couple (literally) cfm more at .500" lift. If you want to fill the cylinder more, first get expert advice from some one like Buddy Rawls or Ed Curtis. It will take more duration rather than lift. P heads flow increases VERY quickly from .100" to .200" and levels out at .400", so design the combo with that that in mind. I'm running 1.6 Scorpions on my P combo.