cylinder head question?/AGAIN

I have a dozen or so old soft cover books, some not so old plus there are lots of sites.
450 to 550 is a big step for a 383, I would go with your #250's for 450hp and eddy rpm's for 550hp.
Check out the mopar muscle web site they did a 450hp 383, it was very basic unported heads, 10.2 comp, 557 cam, mi and headers, enjoy