Welcome to CHR:

I have always loved the 327 as it was among the first engines I ever hot rodded. They buzz to the moon and were always a dependable engine in everything from tri-fives to early Impalas.

Coolant leaks are a bear - one thing you may consider is a leaky intake manifold gasket as water certainly transverses the manifold and with a slight malformation or tear coolant can be sucked into the intake resulting in the symptoms you've described. Your problem may be as simple as tightening the intake manifold to 25 ft/lbs (inside to outside sequence). After that I'd do a complete compression/leak-down test to further isolate the problem. A bad head gasket may also result in obvious bubbles in the radiator fill neck and almost always has steam puffing out the exhaust.

Let's hope you get lucky with the intake gaskets!

Glenn