Zenmuse H3-2D + back-bone ribcage
Got my GoPro Ribcage installed and tested with my Zenmuse H3-2D gimbal.
It fits fine, just used some longer screws to use the default gimbal/GoPro bracket.
The stock GoPro lens plus Ribcage is light enough that with my basic testing the gimbal worked fine. I also tried a heavy 35mm F2.0 M12 lens (15 grams versus the stock 6 grams) and it was too heavy for the gimbal to work. So if you can keep the M12 lens around 6 grams you should be good. Now I just need to find a 6gram M12 lens with no fisheye to test with. I have one but it is too short to focus properly in the ribcage M12 ring. M12 extension tube on the way...