Just a note on the E-Street heads that some people miss.
The stock valve train used in these heads is setup for a flat tappet cam. This may or may not be an issue for you.
Also, the stock valve train is not particularly great. Even though they have decent specs they are a bit deceiving. If you already own the heads and don't mind spending a few hundred extra bucks to upgrade the valve train then it might be worth it. Otherwise, I'd be inclined to stick with what you have already.
Here's a thread about those heads from Corral. Some good info to be mined if you can get past the bickering.
WARNING: Edelbrock E-Street Heads - Ford Mustang Forums : Corral.net Mustang Forum