[Portland68]

That's fair, hopefully the Vortec works out otherwise I'll definitely be wishing I kept it original for my rebuild. Sounds like I will be running a bypass similar to your set up but out of the 3/8 fitting on the front of the intake manifold so I don't have to machine down the temperature sensor, and then intake-core for the heater core inlet and core-water pump for the return (or core-radiator for the correct look) Thank you Jim!