The 2-arm base can be screwed with two M3x12 screws (washers optional) to the Karoo 2 baseplate (just remove the original black screws).
From the Rockbros RHL 400 light, the original adapter can be removed by loosening two small screws. The new one is a tight fit (direction doesn't matter) and has two holes for exactly those screws.
Use a standard GoPro-Screw and hex-nut to mount both parts together.
Another base plate with the 3-arm (standard) is also available (experimental as I do not use it). Please let me know if any further adjustments are needed.
The author marked this model as their own original creation.