Well, if you haven't already done so, check out mustangcollective.com. You'll find some 'interesting and bad ass' 4.0 builds there.
Personally, I would NOT bother building a 4.0. I run a powerhouse turbo pushing 400 rwhp on stock v6 internals (only upgrade is the valve springs). Once you get around 425-450, you need the engine built; but the block won't do you much good beyond 500.
So, yes, a bad ass 4.0 can be done, and a few of us out there have one. (the transmisioin is a TR6060 with an engine adapter plate.)
If you supercharge a 4.6, you can get 450 +/- on the stock engine with a supercharger, and usually be safe within engine limits. Price-wise, you'll find it much easier and cost effective to go the 4.6 route for those power levels. I looked at building the 4.0 in my '05, but the cost, compared to building a 4.6, was not that different. Why build something where your power level is nearly topped-out already, instead of building room to add more power later?
But it depends on what you want to do. Just do you research and know what you're getting into and what it'll cost!