The steel frame mounts: 1" thick plate steel with a little CNC work, and sheet metal steel hemisphere caps TIG'd on. The plates end up being 0.500" minimum thickness, with 1" thick, drilled and tapped, bosses for the four 0.750" mounting bolts. The sheet metal caps, of course, finish the aesthetic; eliminate the need to do a blind, tapped, hole; and save a few precious ounces of weight. After some hand finishing work they should look like cast steel brackets.
My goal was to emphasize the mechanical connection of the big 13 to the chassis. Those steel domes should help pull people's attention down to the area, then the various gaps and radii will offer lots of light-play to bring out the details.
