Yes, it got hot enough to blow out some coolant, about 220 on the gauge.
I had the switches for both the water pump and fan in the "auto" position so my first thought was that maybe one of the sensors wasn't working, but even when the fan and pump were both in the constant run position the temp would creep up. I've got a new thermostat housing coming because the stock one is on the wrong angle, it should be here tomorrow. While I'm changing it I'll test the thermostat and I might experiment by removing it completely to see what happens. At the very least I think I'll drill some holes in the thermostat so that it will bypass some water into the rad even when it's closed. The electric water pump has no provision for a bypass hose so as near as I can tell when the thermostat is closed it can't really circulate the coolant. When the engine was in the Impala it always ran cool but when I was driving it out to the shop I noticed the temp. climbing higher than usual while it was idling. I did richen it up quite a bit last time it was at the track and I've got the vacuum advance disconnected so maybe that's part of the problem.
I know things like timing and fuel mixture can cause a car to overheat. This car has a big rad and you can see the pump is flowing pretty well when you look into the rad so I'm not too sure where the problem is. I'm not all that worried about it because I know we'll figure it out eventually but I'd appreciate any suggestions or ideas.