I'm a bit wary about the integrity of the Pulley Belt fixing. The threaded portion of the bolt is a good 3 mm short, resulting in only a fraction of the threads of the bolt held within the nut. With the correct tension on the belts, the pressure on the bolt/nut assy is considerable. As these bolts described as "M6x20 Shoulder" (should be M5 btw) I really would like to see these as M5x25. That extra 5mm will expose some threads of the bolt above the nut. That can be compensated for with a split washer and a plain washer, making for a more sound mechanical construction. I'd like that plain washer to be oversized too.
The last thing you want is for the frame top to crack !! :-)