Hey Bert,
A company by the name of TabLoc used to make the heads and other things like aluminum sprockets. They were extruded and then drilled and machined for whatever application (Bridgestone, Yamaha, etc). TabLoc sold out to DG, which most people know made the radial heads for many bikes including Yamaha RD400. I don't know if they cool any better then the stock heads (I've run both set ups).
paul