I had 10mm bore shaft motors I ordered from esk8.de which I guess was the start of my troubles because 10mm motor shaft you have to find 10mm pulley (luckily I did just find some 5m 12T 21W 10mm bore on Ebay). There are people selling PETG or 3-D printed pulleys but I think they melt.
As far as the belts, as you can see below the 450mm is too small and makes the engine shaft rub – I did even try to make the 8mm pulley into a 10mm bore but it wasn’t perfectly centered so the orbit is oblong and the pulley useless. Hopefully those on Ebay will come soon.
Regardless the 450mm is still to short and rubs on the shaft after my pulley correction via center drilling the pulley for 2mm more of diameter. I cant even pull it further back with all my strength - I don’t know if a tool like a vice would help. It’s just very tight.
I ordered a 470mm HTD belt on Amazon for a few bucks…maybe that will give the right “wiggle” room.
My two cents