Thanks for the link, more images for reference is good :)
I think you're making it more complicated than it needs to be. A sundial device that small won't be terribly accurate anyway. Getting the inner ring pinned and then the gnomon set 90 deg away are the critical parts, along with the degree markings. If it could tell me the hour of the day, maybe even the half-hour I would be more than pleased.
I started working on my 9x20 lathe again a few weeks ago. I could run it now, but will probably clean up, adjust a few more things yet. If I can rummage up some material for the rings and haven't lost the urge, I may just give it a try ;-)