The key is fixed and the threaded ring free, as far as I can tell. I
mounted the chuck on the D1-6 backing plate, so your idea of removing
the chuck is certainly possible. The lathe bore is about 56mm, and my
only idea so far was just that; to make a long threaded pipe to screw
into the back of the threaded ring to allow it to be rotated whil the
chuck is mounted. I will look at the 2 allen keys again, because I
haven't determined what they do yet.

Regards,
Nick