Here's another option that could be made from a section of U-channel flipped upside down. One could chop off the top 2-3 inches of the mast and use it as a sleeve to attach the mast head fitting to the mast. Of course the numbers on this drawing would have to be tweaked to fit our mast. There is not a very elegant way to attach an anchor light, VHF thingy (can't spell antennae), wind instrument/annenometer though.