I am running the GT40 irons on my supercharged 302. The machine shop work has been pretty extensive (porting, polishing, 3 angle, o-rings, cut for loc wire gaskets). The car is making 403 @ the wheels with these heads and many other mods. I am happy with the performance, but would go with aluminums when I do it again. Trick Flow makes a good head at low cost. You may want to check them out. I would definitely go with aluminum.
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