it's been fiddled with for 60 years, no tellin when or why anything was changed, lots of trucks were sold without heaters and had any old thing added later by the owner - I'd say that bezel shadow looks like a car pattern, could be any make, and in the 2nd pic the bottom of that notch-in-the-hole looks [carefully] hand made to me ... and what's an "electro-vac", some kinda 6V vacuum? or do you mean hydro-vac?
Bill
