We built a drive like this for our 2014 bot. The biggest difference from what you're planning is that we used #25 chain instead of belts. I'll upload our CAD (w/ a full set of drawings) when I get home tonight so you can see how we mounted the TB minis. We ran 4" x 1.5" Colsons on live axles with the TB minis geared 8.45:1. You will need the long hex output shaft (am-0801) for this design.
Here's a pic to give you the general idea.