^ is a nice roller (Cabuss' 91 GT).

As aforementioned, best mods for the 4.6L will be gears, headers + h-pipe, and a power adder!

My uncle & cousin have an '01 Cobra (4.6L DOHC) with a Vortech on it, and it's freaking awesome. But not sure that something to that effect will be in your budget or not.