Gunmoto was able to fit it after getting that pie cut in the y-pipe and welded back up.
I did that for another guy but he hasn't fitted it yet/got some serious strain in the setup.
It is not plug and play. If you want to fit it to your 1299/959 bike, I recommend having a fabricator / welder assist you and take care of the measurements and fitment, as well as the cut in the y-pipe and the welding of that.
I can also offer to have it sent to me, setting it up in the fixture with the y-pipe and adjusting the angle.