Dont forget about that bottom end. How many miles do you have? I know that probably from what everyone's said about mustang bottom ends taking a good beating you'll be ok with your combo, but if you havent touched that bottom end you should really consider it. It would be a shame to fly down the track to have a piston blow through your motor, or even worse your brand new heads.
But if you have built the bottom end, forget everything I just said...sounds like a good combo, dont know about 400 horses though.
And if you change your fuel injectors, dont forget to change your mass air meter.