I posted a question a few weeks ago about the best place to mount the bearings in a backshaft setup for my Taig lathe and the responses helped with the thinking.
The gadget is now finished(? are they ever!). In case anyone is interested in the approach, I have added a few photos in my Taig Lathe album.

It works as designed. Gives me a 10.5:1 reduction between the motor and the spindle, and gives good useable torque at the spindle down to about 50rpm.
Again thanks for the advice given here – I am learning a lot as I go along. I now have a new list of things "I wish I hadn't done that way" but must confess the lathe has become a project rather than a means to an end.