364V8 overheating, especially when ambient tempurature is over 75. Flushed engine, replaced waterpump, hoses, belts, t-stat, new overflow bucket. Has a new radiator/cap. Has AC, but not ever used. BUT, there is steam coming from defroster vents when it gets hot and you can smell coolant, creating film on windshield. I do not believe there is any blockage in heads, as I have had them off. Distributor seems to be stabbed correctly. I believe heater core is beginning to leak or may be clogged and this could be the problem. Can I bypass Heater Core by attaching a short hose from inlet to outlet port on waterpump? Any advice as to how to close off heater core completely?

I don't know how a bad heater core would cause overheating but you are right its shot. I bypassed mine by taking 1/2 inch electrical conduit (pipe) bending it in a "U" and disconnecting the heater core right at the fire wall. You will still need to get it out. I left mine in and when I finally replaced it everything was a rusted mess. My bad.

If you have steam coming from your defroster vents, you definately have a bad heater core..!