Three things stand out.
First, I doubt you'll have any where to rest your wrist while using your spinner based on that picture (looks like it will be resting right on the buttons which could cause accidental triggers). Not sure there's room below your joysticks for your wrist to sit.
Second 6.5" is pretty shallow, particularly with a trackball. Not sure how the rest of your cab looks, but I'd be very worried about hitting the trackball and following through right into your monitor screen.
Finally, at least as drawn, there is no room for the control panel box below the buttons/sticks. Not sure how to best explain this, but since your joysticks/trackball go right up to the edge of your top panel, you're not going to be able to build a box for underneath without either the base being bigger than the top, or your joystick bottoms sticking out. If you look at other samples you'll see room left for an overhang beyond the base of the joystick. You should have at least 3/4" (or whatever your wood width is) unless you're not building a support box at all.