Get a piece of 1 1/2 diameter aluminum, 2024 if you can..
turn a .749 diameter 3/4 inch long on the end..Cut off so about 1/8 inch of the 1 1/2 diameter is left...Drill and tap for a 3/8 grade 8 bolt...Drill the 6 holes for mounting with flathead allens..
countersink the holes so the mounting screws are flush...Plug the .749 end into the hub and put the flatheads in with some Loctite...Coordinates for the 6 holes are + and - .562, + & - .281, and + & - .487