Looks like the belt is a 142-2GT. That comes out to a 142mm length GT2 style belt that measures 6mm wide with my calipers. The gears are 16mm OD, 5.95mm ID, with 20 teeth per gear. (The ID of the second gear looks to be drilled out by hand bigger to fit the z-axis lead screw). Hopefully this will get you going in the right direction!