My guess is that the 357 heads would be a tad big on a motor looking to make 600hp at the wheels and you may hurt some hp. I would consult with AFR before picking your heads. Also, 7400 rpm is high with a big motor like that. keeping the rpm lower will make your motor live longer and you can easily make 600+ rwhp without going that high.
I have 2 buddies that each have 540's that made about 795hp and the other about 805 hp on pump gas on an engine dyno. If your interested I can call them and see what heads they are using.