Vertex Universal Dividing Head conversion?

I have a virtually new Vertex Universal Dividing Head and from time to time consider converting it to a 4th axis. Having the angular axis seems like it could be very useful. However I am concerned that the backlash issue would be a problem. Should anyone have done this conversion or converted a Vertex circular table. I would be pleased to know the result. Other option is Chinese harmonic unit and again if you have tried one I would value any feedback.

I have a Chinese belt drive unit which I re-engineered with shaft support bearings and a belt tensioner, with a steel re-enforced belt it has no backlash and has the potential for decent through capacity which the harmonic drive models cannot.

Didn't John S (hobbnob avatar) do a parts for the conversion of said rotary tables?