Well great minds (OK – this maybe an exageration in my case) think alike Michael – I was just checking the belt used on my Taig milling head.
It's a 'Gates 3M315' – 3mm wide/narrow and very strong. They are available in various lengths – so yes – I think that would be a very simple way to do it on reflection. Also some form of 'gearing' (2:1) on the pulleys would help increasde the torque available.
So that's sorted then – you design it and I'll build one!
I'm pretty sure David would also like an article about it in MEW too!
IanT
PS Looked at the JAFMotion device and it seems to fit the bill – and it's even within my price range – even better!