[Nickthedentist]

Would the top of that bezel perhaps have been glazed?

Have you Googled the former owner?

It looks home-constructed to me, or at least made by a garden shed type of manufacturer, and probably modified/modernised over the course of its working life.

Maybe best to remove the (1970s?) mains lead (or entire mains power arrangement) and sell as a objet d'art rather than as a potentially-working machine for giving shocks. Someone with enough knowledge could then put it back to its original purpose, but your average purchaser would probably just put it on display in their man cave, hipster pub, barber's shop or whatever. I'm usually very much against "steampunking", but I wouldn't feel too upset about someone doing that with this.