OK, here's the deal. The drivers side is the big problem. I have tried several types of headers and so far, nothing fits. The strut tower is just in the way. And its 1/4" steel, so forget about bending it! As Todd says, the studs/bolts are the major concern, they break. Now supposedly Ford has upgraded the bolts? I have been battling exhaust leaks for 6 months now, so I know whats going on.
Now, the headers you describe are for a 2-valve motor, ours is a 3-valve motor. Big difference! There is only ONE possibility left. Ford Racing makes a "shorty" header for the Mustang 4.6L. It might have a chance of fitting, but I've bought so many different headers that I thought would fit, that I'm out of money. So I can't say if they will. Plus, you really don't gain all that much with headers on a stock motor(5 to 20hp). Long tube headers are the best for making power. And there ain't nothin' that fits! So my advice is, if you have the money, check out fordracingparts.com and look at those shorty headers. Buy 'em and try 'em, then let us all know if they work. I know of at least 3 people who are dying to know! But DO NOT damage them in any way(even scratches) or you won't be able to take them back. Listen to someone who has tried. Doing a true dual exhaust with the stock manifolds has been the way to go so far. Good luck and stay in touch, Bob