No coolant temp sensor on a 79, or computer. It's either going to be the coil breaking down when hot or a bad spot in the starter. If it cranks over good but doesn't fire it's most likely a coil going bad, but could also be that rotten "electronic ignition" module. (I hate that damn silver box on the fender)

No that I think about it check your timing too, to advanced could cause the overheat issue to a point too.