Bracket on a curved transom

[McGillicuddy]

There are any number of "wacky-wood," bending plywood sheet products that you could use for the leading edge of your bracket mold to accommodate the transom curvature.

Use a scribing tool to mark your lines on top an bottom to nail down that radius for your horizontal panels.

Heck, I think one of the brand names of these sheets is "Radius." Do a search for bendable plywood...