GT40 or GT-p 40 heads .... in my opinion, are OK, if you can pick up a set at the junk yard or a swap meet, for cheap. they make a fairly good step up from earlier stock heads. Of course theres the issue with headers, spark plugs and the lack of smog fittings for those with the early HO 5.0 liter that use the EGR pump.
If you are going to spend real money, then I agree with all the suggestions to get the World/Dart/Rousch heads. Whether to get the Sr.'s or Jr's...is an issue of how honest you are with what you intend to do with the build. 289/302/306 (.030 over 302)...can get along quite well with the Jr's. the 1.94/1.60 valves and smaller combustion chamber work great. If you have extra money (or talent) then a session with the Dremel will provide all the flow you need for a N/A engine. If you are going with a stroker, then you probably want to step up to the Sr's (2.02/1.65).
There is no question that there is a lot of attaction/glamor to to having the Aluminum heads, they give you instant status once the hood is popped. But, I am still not completely convinced that they are any better at making horsepower than the aluminum heads. The debate over aluminum or iron heads, at least for me...is mainly whether taking 40 ~ 50 lbs off the front wheels is worth twice as much. there are other arguments: aluminum is easier to repair, more tolerent of high compression...OK, thats true. But, they are a hella lot easier to cross thread spark plugs, easier to strip or wear out threads and need to be handled "gingerly" because the metal is much softer. I have both, and have long resisted the knee-jerk reaction to immediately tossing the iron ones, ...mainly 'cause the iron ones haven't given me any trouble and I don't see where I'm losing any power, I did have a pro - porting job done on them, but thats another story.
Unless you are running "class racing" I'm not a big fan of chasing rainbows. The "Ultimate" flowing, "Best" super dupper, flavor of the month, magazine special featured head will always be The next head or the one that you don't have. I don't know many working for wages guys that can afford to swap heads every few months...I admit, when I was younger, I didn't feel this way - I chased after the "magic bullet" too. But, when you get right down to it, tunning what you have will usually find more horsepower than constantly changing components and having to re-learn what works for your setup. Tuning takes time and observation to get the best out of a combination. Every notice how, despite the restrictions...most stock class cars are making better times than a lot of "street Heros" who have access to all the hot parts? What the time now on Stock CJ Mustangs..aren't they in the 9's. Running stock factory parts, iron heads and limited engine sizes...How the heck can they do that?
"They that can give up essential Liberty to obtain a little temporary safety deserve neither Liberty nor safety"-- Benjamin Franklin
<font size=-1>[ This Message was edited by: Beoweolf on 3/9/06 9:40pm ]</font>