The hottest water from the cylinder head should circulate to the heater. Generally that would be the lowest heater coolant inlet. Since hot coolant tends to rise the outlet should be the hose to the water pump where the coolest water flows into the engine coolant packages. There might be a little flow to provide some heat to the passenger compartment and cool water to the engine to reduce the temperature increase when the pump is not circulating coolant. Many of the earliest motor vehicles used this therm-syphon system before pumps were introduced.

The layout will probably differ some, but on my 1935 and 1936 Chevy engines, there is a plug for a heater hose connection, just below the thermostat. The stat acts as a baffle to force water toward the heater. I believe this water enters the lowest heater pipe. The water is returned to a fitting in the water pump.

I think this agrees with Chips post.

Mike