Heater Plumbing

[GMC KID]

I have a 1962 GMC 920 it's a Canadian built 3/4 ton with a 261 ,and yes this is the original engine that came with the truck,numbers on the block match ID tag in cab.the question I have is the heater was never hooked up since I purchased this truck, the heater core has 2 different sized water lines ,1/2 inch and 3/4 inch. The 1/2 inch is on the water control valve side, which size goes to the water pump? I keep reading articles this engine didn't come stock in trucks under 2 ton size, maybe the Canadian trucks were the exception .

[Pre68Dave]

The larger hose goes to the pump.