I lucked out when I hooked up mine (1960, 261; dual Offenhauser intake w/Rochesters and Fenton headers). The original water pump had two plugged holes (the engine had been in a large school bus), I assume for a second heater's supply and return (both holes on the "under side" of the thermostat).
Two other options (that Tom Langdon told me) are a GMC thermostat housing (one outlet under the thermostat, on the intake side of the engine) and/or a plate he sells that goes between the thermostat housing and the head (I have used it - no clearance problms).
Tim
