Measuredm traced out and installed the left wing nav/strobe light bracket. Centering the bracket was easy, but after drilling the first attachment hole into the fiberglass wingtip, I became concerned about the wingtip's ability to hold the bracket reliably. So I fabricated a back plate for the bracket out of .025 aluminum (same thickness as the wing skin). I think this will be more durable.
The left wing tip with the nav/strobe attachment bracket pattern traced out on it.
The nav/strob light installed.
Inside view of the nav/strobe assembly with the fabricated back plate.