Sounds like the stock vacuum switch setup used from 1955 2nd and up. Is it mounted to the top of the transmission on the drivers side? The ones I've seen have 4 hose ports. 3 large and 1 small. The 3 large ports are for Main Vac Supply, Hi to the rear and Lo to the rear. The small port connects to the 2-speed adaptor on the back of the speedometer which keeps the speedometer in calibration when you shift the rear from Hi to Lo and back.
All of mine are natural metal color, not black, but yours could have been painted at some time.
Pictures will help...
Mike B
