If you're certain that your problem is ignition related, check the ignition. I have a
Pertronix and it's wonderful, but if you feel you have a problem with it, look in that direction. Bad
coil? Don't overlook the wires and distributor cap.
That being said, there's a known common problem with heat-related rough idling and stalling that's
carb related. I believe your original
carb has a spacer plate. I have an
Edelbrock carb and manifold, and had this problem really bad until I bought a spacer plate to install under the
carb. Big improvement, still has done it when it's hot out, but after a good
radiator clean, the motor runs a bit cooler and this issues seems to have disappeared.
The issue has to do with the gas -- it's now an ethanol mix, which has a lower boiling point than straight gasoline. The combination of this, plus the
carb getting a little hotter than it should, add up to gas boiling in the bowl, causing rough idling, stalling, and even a gas smell after shutting it off. It's at its worst if you stop at a store, then get back in the car to try and start it., It's tough to back out of that parking space!
Something to consider!