I respectfully disagree on a couple points.
First, replacing injectors is unnecessary unless you're making too much power for your current ones, or you have a bad one. They're simple devices, and not that highly prone to failure. The stock size (19#) is rated for up to 300bhp, but that is at a 90% duty rate, so a bump to 24# in a full bolt on car isn't ridiculous. Otherwise, save your money.
Secondly, "pretty damn quick" is a matter of opinion. We're in an age where V6s put out the kind of power that a bolt on 2V does; for many (myself included), the recipe above is going to disappoint. Of course, that depends entirely on personal preferences and goals, but mine include being competitive with stock V8s (but, my brother has a 15 GT too).
Thirdly, there is no reason to fear boost on these engines. They're strong enough to take reasonable levels in stock form, and can easily be upgraded to handle more. There are countless examples of supercharged 4.6s daily driven with little to no issue. That said, for the power range you're after, connecting rods might be a good idea. Most say they're only good to 400whp. Coyote rods can be had pretty cheap as an upgrade (I believe they're less than $200 for a set).
Bottom line: You're not likely to break 400whp on a 4.6 2V NA. Your options are: moderately upgraded 4V (cams, intake, head porting and etc), or supercharged 2V.
Best Trick Flow could do is 466bhp (~390whp) with a 5.3 big bore stroker that costs over $11,000 to build (Summit sells the kit). A Supercharger kit is half that, and will out perform it.