the two holding holes have to be drilled M5
the belt tension screw hole has to be taped M4
the holes to hold the belt on the clamp and on the extra bit have to be drilled 4mm if you have the nuts , or you can tape them M4 eventually (but i didn t try)

and if your print has a sharp edge where the belt rest on , it is advised to fill it a bit

i have uploaded a second file where the resting surface of the belt is one milli lower and it might align better with the smooth idler wheel
this hasnt been tested but should be closer to a perfect alignment