Weird ignition problem...maybe!?

This is a '73 Dart with stock electronic ignition and a 318 with Edelbrock. This started a few days ago. After the engine warms up I can be sitting at a light or at full speed on the highway, and quite suddenly the engine dies. I check to see if it's getting gas...yep. So I check for spark. The one time I did this I was on the side of the highway in rain, so I'm not sure, but I couldn't see any spark (plug wire end about 1/4" from ground) at all. There is no problem with cranking when this happens. So I let it sit for about 20 minutes and then try it. Starts right up. Five miles later it dies again. Same thing...let it cool and it starts. This doesn't happen until the engine is warm. The choke is fine.

When it dies, there is no flutter like it's run out of gas, but just a very quick death. I have come to two conclusions; 1. Something in the ignition (the control box?) is overheating and dying, then coming back to life when it cools. 2. The Edelbrock carb (1400 series) is leaking internally and flooding the engine. But again, it doesn't flutter to death like a gas problem would, just immediate death. And that wouldn't account for the lack of spark.

So, any ideas?