I'm looking at my dyno sheet from my old 548. It made 793 at 6,700. It was similar to your build, but I did have a set of aluminum heads c&c 'd by RFD. They flowed 400cfm at .800 and I did have a vacuum pump.
I doubt with those heads you're gonna get into the 700's, but I'm not fimilar with them. Even though you have to run iron heads can you run a vacuum pump and a dry sump? Not cheap hp, but you gotta do what you gotta do to win!