http://prntscr.com/1m24bi
I was doing some more messing around and found that if WCP would have made their gearbox a little more than an 1/8th of an inch wider maybe more like 1/4", we could have fit 5mm gt2 pulleys in there that are 9mm wide. It is so close. I wish WCP would just make a version of their gearbox for people like us who like to use belts...