I decided the BMW rear rack for my 2009 R1200R (K27) was too expensive and designed my own mounting plate to use an SW-Motech Adventure Rack. Here are results.
I ordered the Top Case Holders (#6 in picture below, left and right from Max BMW). Mounted them on the bike in order to measure the hole dimensions. Also ordered the Adventure Rack for a 2020 Honda Africa Twin because it was on sale at Revzilla.com. Next, I used an online machineshop (emachineshop.com) to design the mounting plate. They do powder coating also. Ordered all the mounting screws and spacers from belmetric.com.Looks really nice! How'd you do it?
If I get any interest I could do a small run. Message me if interested.Looks great Jaalfs, and the finish on your custom plate looks great too - it could almost be mistaken for OEM.
It wouldn't surprise me if there were a few folks on here keen for you to make and sell these. Could be a nice little side-hustle for you.