Matt,
There was a different generator panel for the single speed, but it was never fitted to Ferrets. I think it would be easier to put the system back to how it was intended, replace the single speed generator with the 2 speed. I'd have a look inside first and make sure it's all ok, otherwise see if you can get a specialist to look at it. You can get the 2 speed generators and panels quite easily if you need replacements.
Chris