A guy on.org made an aluminum billet race head about 5 or 6 years ago and had good results with it above and beyond what was done on that same engine with a maximum effort stock cylinder head. So its being done more and more as people get more ambitious and creative. I could do a billet head as well, but it would be so expensive compared to a new cast head nobody could afford it. It just all comes down to what tools and skill set a person has at their disposal to accomplish the tasks at hand.