We set up steering drive 1:1, so that steering drive angle provides an accurate proxy measurement for pivot driving angle.
We also used chains/sprockets and belts/pulleys to provide our gear reduction. Drawback is no gearshift (yet). On the positive side, we've got no formal gearbox.
1640 has been running pivot drive two years now. We are pretty satisfied with how it works for us.
The very devil is the control software. We spent a lot of quality time on developing this.