this is the typical german setup !
German TÜV-regulations from the 1980s didn’t allow to mount the rear flashlights to the frame ends as elsewhere in the world.
I’m sure to find a “good” one in my stock, but have to travel for the next four days.
You will only need the metal base, we may call it the “rear cross”.
Your stock rear light and flashers can be fitted to the “rear cross”.