After the temp drops to normal, I can drive it all day long and it does fine.. This is what makes it interesting and seems to rule out anything "serious"

Sure sounds like you have an air lock, but I would try some more detective work before tearing into it..

Running without a stat

Make sure you have a shroud and rad is sealed good to rad yoke

Put a fan in front of rad and let car run see what happens

Make sure you have the right pulleys

Any chance you are using a 440 source wp or wp housing, they have had issues, also some of the blocks had a mismatch between the front coolant holes in the deck and the head, but I have only heard of them being oversized, not small.