Eric, the combo I listed up at the top of the thread should get it done for you with those heads. RB block, 4.250 crank, 6.80 Chevy rods, Diamond flat tops, flat tappet cam.

Add another grand for a roller setup and you'll easily be at 750 hp. Since it is a race only car you could add some small domes to the pistons to push the CR up to 13 or 14:1. With that big stroke you only need a tiny dome to really crank up the compression.