I had a belt drive similar to Lawnmowermans, I gave it to a mate who made a rear carrier for me, I think it was made by a bloke about Durham somewhere, trades as Sappy on Ebay IIRC, anyway my mate seems to think it works ok although he had o cut the cork washer in half to get the big pully to stay on.
Now you guys got me wondering about that small pulley, I can remember fitting it on the dynamo on the bench, can't remember taking it off again to fit the dynamo.
I have a spare inner case and a spare pulley so I'll compare tommorow.