That depends on what water pump you use. The Vortec block I built had the passageways and with the older water pump, simply drilling the head provided for the correct coolant bypass. Actually if...

I am talking about adding one to what already exist via the heater core. On the carbureted 350 Vortec I built, it had the bypass hole and passageway in the block. I simply drilled the Vortec head...

You do not need a bypass of any kind on a stock TBI cooling system. The heater already bypasses coolant from both sides of the heads back to the radiator if you run the GMPP intake. I never ran a...