i needed a mount for a modular design on the new tail, everything would be hung from a base plate, had to be solid, unlike those little tail tidy kits. i had one of those in the parts bin that came with one of the donor bikes, functional, but not what i wanted.
so i started here...
the plate has mounting studs going both directions, plus SS threaded anchors at the corners that line up with the new mounting points welded to the frame. the plate is sized to fit the indent in the OEM fender liner.
the studs are all welded in place, and it's much easier to keep everything straight if you thread the holes in the plate first, screw in the stud, then weld.
again, there's not much room back there if you're using the OEM tail light and seat covers, takes some planning.