The Andy Mark KOP drive base for 2013 used belts. Take a look at the list of components and the CAD.
http://www.andymark.com/AM-KOP-2013-s/451.htm
We used the base and the kitbot on steroids tips and we had a excellent drive base. I like how the belts were center to center distance and the belts were self centering. The Andy Mark folks did a outstanding job designing the KOP drive base.