Ok, I think I have the focuser driver taken care of. I found a couple threads that were really helpful - particularly nMAC's reply here:

http://indilib.org/forum/focusers-filter-wheels/2355-stupid-question-on-dc-focuser-stepper-and-autofocus.html#17635

And this one that covers the Moonlite protocol:

http://indilib.org/forum/general/283-moonlite-focuser-protocol.html

Based on those I was able to make a Python shim that impersonates the Moonlite hardware, using the time the servo has been powered on to synthesize an amount of movement.

I can share all of this if anyone is interested, but you're best off waiting a couple weeks until I can fully test on my own hardware.

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