Ok... think I've got this. Was an error causing it to be a bit offset.
rebuilt it. Bare with me, I haven't taken a cad class or messed with cad since 1994
This version is 27mm deep below dash. I think that should work. At least for MOD rovers. There might be junk in the dash on more fully appointed rovers.
Also added a 1" ball mount for a RAM style arm. Just a work in progress.