cylinder head temps.

230-240 degrees seems kind of hot to me. Is that from idleing in traffic for long periods of time? The aluminum heads will help make your engine run cooler, because they dissipate the heat better than cast iron. But I'd work on getting your current motor combination to run a bit cooler before purchasing some expensive aluminum heads. Like you mentioned...you don't want to damage new alum. heads. I'd replace the stock clutch fan with an electric or flex fan. The flex fan I run moves a lot more air, and made a difference in motor temp. Some other things that will bring the engine temp down would be a plenum spacer. That goes between the upper & lower manifolds. A bigger, aftermarket radiator, preferably aluminum. And last but not least Redline Water Wetter, which you add to your antifreeze. All those things helped my motor run much cooler. I never used the Water Wetter on my current setup...but I have on past Mustangs I've owned. It does work.