Quote Originally Posted by lionelhutz View Post
Yes, the bypass uses the heater core exactly as explained in my post and the referenced post. You muddied up the requirements for a bypass by posting the "you do not need a bypass of any kind" statement regardless of the intention. On a Vortec engine (not just using the heads but the newer block too) there MUST be an external coolant loop in place to perform the bypass function. The OP also asked about NOT running the GMPP manifold.
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 you simply use the Vortec heads even on an older block it will block off the bypass!