Tom, did you have any trouble with the central encoder shaft, re; length?
After I put 'Ebony Star' on my Meade, the shaft was 'just' long enough to get 2~3 turns into the bottom plate.
Do you use a 12 volt battery for anything at all, heating/red leds etc? If so, then why not make a 'fixed, 8.5 volt, regulated' supply for the control box? Only need 5 or 6 components. Keep it small & there's just enough room inside the box. I simply soldered the components, point to point. (no pcb or veroboard), & put the socket on the opposite side.
see pics......
HTH.

L.