Davey's pics on his post pretty much show what he did, I made my adapter from 3mm carbon fiber plate I had leftover from another project, but it is shaped as his pic shows. I think the Ion bracket he used (and I also used) was for a Honda 600, part number 106 if memory serves.
No plans, just trial-and-error fitting. Takes some minor fabrication skills. Took me six hours start to finish. Yeah, I'm no fabrication genius😄