I'd like to know more about that smaller diameter section at the bottom of the pulley boss. Is it part of the pulley, or a separate part? There is also a mysterious joint line around the end face of the boss that needs to be investigated, along with the flat on the outside of the boss about halfway along it. Can we see the boss from some other directions please? Is there a matching flat on the opposite side of the boss? Can we see an end view of the keyway in the shaft and boss? There is a missing detail here somewhere. Some of what I see suggests there is a pinching (tapered) collar inside that boss.
