Re: C3 pulley inquiry requested by vendor: "If new pulleys were made I would..."
You have to look at the design parameters, CrossfireKat said that machining the OEM pulley down to the C3 diameter was not possible due to the groove inside the bore. If the groove was not there then presumably it could be machined to the C3 size.
Would it be possible to machine one smaller? Probably not or the C3 could have been made smaller is my guess and with the diameters of the bearing and the hub on the SC remaining the same then a reduction of the C3 size may be not feasible.
What is the wall thickness on the C3 between the root of the belt grooves and the largest inside diameter? That is the size that would determine the feasibility of going smaller. The belt grooves could be made shallower to the bare minimum if they are not already at that size.