Steve, A simple way to mount that mast head fixture is to use a standard mast bracket inverted over the halyard wheels that rise out of the top of the mast. It could be rivetted onto the mast. The hard part will be to find an aluminum mast bracket. All I've ever seen are stainless steel. Stainless steel and aluminum don't go together well. You might use aluminum brackets available at a Lowes or Home Depot type store. Although your mast is already a great lightening rod, your lead would facilitate the flow more directly to your terminal block, presumably inside your cabin. You might look at interupting that flow with some kind of safety device and directing any stray voltage over the side. We've recently experienced lightening strikes 10 miles away from the edge of a storm. Scarry stuff. Stan M-15, #177