Just build mounts that are adjustable. I saw your gif, I agree, find a bolt that works and is long enough to access the fitting, and then design the mount based on the bolt that fits. You can also find "all thread" rods instead of a bolt, that route may be easier if you are OK with cutting and filing all thread.
As far as mount material, wood should work fine if you can work with that.
If it were ME, I would get a bolt or all thread as mentioned, then I would design my mount in CAD software, then I would make a high-quality print with my 3D printer
Any chance you know someone with a 3D printer and CAD experience?
The other option would be to hit up KEF directly and see what they tell you (i.e. cut the dealer out of the conversation).