I find this very interesting... I wanted to start with my cast iron heads... then later switch to aluminum in a about 2-years... but I was told that my pistons (-20 dish) dictated cast iron heads only because of the lower CR (~9.75:1). I've since installed the cast iron heads, and also cc'd chambers and cylinder... calculated the CR at 9.9:1

I'd still like to eventually swap to aluminum heads... per allowable racing class rules. Cast iron allows me to run in more classes and be more overall competitive, but giving up a little to the classes which allow aluminum heads.... weight is factor for me... more than engine power.