I like the 470 inch combo in a 400 block if you are going to use standard port heads. Not too hard to get 600 hp if you use the Trick Flow heads and the 400 block takes up a little less room under the hood.

If you decide to go that way I think member Airwoofer has a brand new Molnar 470 crank for sale. If you buy the crank from him then I'd add some 6.700 long rods (Molnar is a good choice) and then some 1.32 CH pistons. I used Diamond shelf pistons in my 470 and they made 10.6 compression with the Trick Flow heads. Super nice combo that basically falls together as long as your block will finish hone at 4.375.