I'm not a 5.0 expert, but I'm pretty sure they can handle well over 300hp on stock internals. They stand up to boost pretty well too. Very stout power producers.
Yeah 600Hp is the usuall number you hear, but just keep in mind it's not horsepower that kills engines, it's usually detonation, you have to especially have to worry about that with turbo's. But as long as you now your car and keep it in good tune and it always has good fuel pressure and everything is in check and balance, I think you can push past 600.
However "escort?" i would change to fordged internals before turbo charging a 5.0L.