Rob perhaps we can gain access to the Johnsonian design now that they have closed. There design was unique in it permitted latitude adjustment.
Shaun, your very closely following my old post pattern. I went through the same alt/az motor, equatorial platforms, eq6.. finally I gave in to the Meade Goto's.
Have you considered Mel Bartel's Servo system or Mel and Dan Gray's Servo system.
http://www.bbastrodesigns.com/BBAstroDesigns.html
http://www.siderealtechnology.com/
Dan Gray's system Sidrealtech works well with Argo Navis as its brains.
Regards.
Fahim