[Arran]

I checked my Northern Electric chassis, the American Bosch clone, and while it isn't exactly the same, three bands instead of four, it uses a simialr sort of band indicator. They used a length of heavy duty (thick) dial cord that was wrapped around the hub of the indicator and a pulley of some sort on the band switch. I didn't pull the chassis out but there does not seem to be a provision for using a belt on mine, no tensioner pulley or groove to speak of.
Regards
Arran