I would like to know the spindle speed and position, in order to do
rigid tapping.

My spindle can be connected to the pulley straight of through the back
gear.

On top of the head, the pulley shaft is hollow and I can mount
something in there, but then I would have to account for the back gear
and it is slightly messy.

I believe that Jon Elson somehow mounted his encoder to a gear inside,
which seems a little painful.

Does anyone have a good idea?

i