Water pump to intake size

Rick Ehrenberg sells the correct nipples on eBay if you don't mind spending $24 for them.

SB-Nipples.jpg

As you can see from this photo, there are two fittings on top of the waterpump. One is to supply water to the heater core, and the other is the bypass hose which goes up to the manifold. The pic says for 1970 and later, so maybe earlier years are different??? Anyway, you can buy a brass reducer bushing to convert the 3/4" thread down to 1/2" if needed.