I really should update the blog.... came to the same conclusion that you have, and went back to the drawing board. I'm leaning towards some large taper rollers and a 90mm stub shaft at the moment, but the limiting speed on them is 8600RPM, which is what we're (hopefully) operating at, so not quite sure how it's all gonna work.

Drum Design 8.PNG

We have space for a larger V belt - it's an SPA on there at the moment, but we definitely have space. I have the CAD for a 40mm PCD pulley, up to 3 groove