Well, I received the new brake light in the mail today, and couldn't resist digging in.
Bent the light bracket to 90 degrees and used the license plate mount to attach to the tool box studs on the bottom of the seat pan. Had to slightly lengthen the slots on the bracket to mate with the bolts, but only a little. Spaced it off the seatpan with a single nut on each side. Left enough stud for the bracket, a washer and another nut.
Working on a new seat for it, and have flush mount signal lights coming which will go on the frame where the grab bar bolts used to go through to the rear fender. Signals mount with adhesive - will route the wires through the existing holes in the frame.