The heads don't need any porting, maybe get them a valve job and cleaned up if you are feeling froggy. I'd just run it with a safe tune at 600whp. You'll need a ****load of driveline/suspension upgrades on that chassis to reliably support that sort of power on a 04-down car tho. I'd do all that stuff before adding more power TBTH. Or you'll just be spinning your wheels or breaking things.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.