Heater Hose Tube on Radiator

[jec]

Getting ready to install new heater hoses on my Longhorn 402 big-block. Truck has no A/C correct factory heater box on firewall with 3/4" core tube on top and 5/8" core tube on bottom.

I have the normal 5/8" fitting on top of engine manifold near thermostat housing. This supplies hot water into the bottom of heater core.

I have the normal 3/4" fitting for a return from the top of the heater core to the side of the water pump.

Any ideas why my radiator has 3/4" Male Heater Hose Tube about an inch below filler neck pointing straight out toward engine?

Maybe it's for an auxiliary heater return or something?? I can't think of any purpose for it. Maybe somebody knows or has seen it on other trucks.