Hi Colin,
I think I see where you are heading with this - what I cannot foresee at this point is how you are going to seal the ball-race against dust/dirt (which would bring it to a grinding halt in quick time) and how the turret will be kept on/in place.
I should be patient and wait and see, of course, as I'm sure you already have that worked out ..... but I'm not (patient, that is).
The speed at which you are working on this build is a bit intimidating. I'm only working on one little Ford GP, and taking years to do it!
Mike