How easy to get 500 horsepower w/ stock stroke 440?

I would say you might want to solicit the advice of someone like MRL...one of his hallmarks is making good hp, with a very livable idle (which includes decent idle vacuum). Much of that requirement will deal specifically with a combination of static compression ratio, cam timing events/profiles, and how well your heads flow...but you probably already knew that.

EDIT: oops! I just saw the link poison posted...the 440 MRL just put together drew 15" Hg w/o vacuum advance, 19" with...think the OP might have an example of what works there...