There are options in head materials. Aluminum is lighter but has more heat going straight to the water jacket and subsequently not being turned into energy (horsepower). But improved air flow as well as a compression increase can compensate for this. On the other hand, iron heads would be good too especially if the flow numbers are increased and even if the combustion chambers stay at the stock 69cc ‘G’ size.I’m assuming that the head manufacturer will have final say in the material being used but will be nice if the heads are designed around the material. I’d personally hate to see another fiasco like the Edelbrocks for the Fe where there’s a drop in performance using the aluminum head over the factory cast irons only because there was not an accompanying increase in air flow and compression ratio to go along with production of them in aluminum. Referring to out of the box and unported of course.