Just as a quick thought, I would think if you can get oversized valves, every extra mm in diameter you can get will help. Especially if you have thoughts of going as high as 450 hp!
I think I personally would be more than happy with 350 FWD! I'm considering a LS3-480 in the Mazdaspeed Miata down the line, and even with RWD my friends laugh at me for thinking I'll do anything but light tires on fire when I try and accelerate!
If you want to daily drive it, 350 hp might be more than plenty. I've seen pics of FWD drag cars that can put that kind of power down, but you can't drive to the grocery store with those crazy wide wheels and non-DOT tires.
Might be worth a call to Tom, I am pretty sure he's done this kind of thing multiple times, he might be able to offer much better advice in regards to the head, crank, etc.