ke70dave: the heater core is in parallel with the radiator, it bleeds some of the water off the cooling system and returns it, it's a restricted flow and it cools the water so it has no issues. However if you just bypass it you have a 5/8" pipe that just goes from the top to the bottom radiator hose. I was wrong before about one thing, the top pic is wron but only if you dont look at the crude crawing of a heater core in the system.
keimeier: have a look about the heater core drawing in the first drawing, I will draw you a diagram