QU-BD X Carriage for Prusa Bowden Mount

I finally moved to a Prusa style bowden extruder for my QU-BD Three Up. This is one of the final modifications I made to the printer before retiring it. It allows belt tension adjustment by pinching the belt between the teeth on the back of the carriage. It also allows the left and right sides to be be different heights to accommodate the height differences between the x pulley and right side bearing.