WIW X-Heads

X heads are an open chamber head; to achieve your goal of 400 to 430hp is gonna require port work, not a lot but some.

Go back in the "Mopar Muscle" archives about 12 to 14 years, Dulitch built a 360, he ported the heads (587 castings I think), with a Comp Magnum 280 cam he dynoed out around 430hp; in the zone you hope to be. It would be good reference materiel to help you get where you want to go.

What ever you do, good luck.