On a '55, it mounted on the core support panel just to the left (driver's seat looking forward) of the radiator inside the engine compartment. If the '56 is the same, and I think it is, there will be three holes in the panel for the mounting screws.
Man, my apologies. I have been forgetting to take the shot for two days now.
attached is the typical 56 wiring diagram. Voltage regulator is #10505.
Regards