You might be able to narrow down your problem with a hair dryer.
I had a 1974 Datsun 260Z that would not start on cool mornings and it turned out to be the electronics box up under the dashboard above the passengers feet. I'd just run a propane torch over it for a brief second or two and the car would start immediately. And I sure don't remember how I figured that out.
And for another problem I had as a kid. An old dodge would occasionally just quit running. Stop dead. The problem turned out to be in the distributor. It had dual points and the insulation wore through on a wire pulled tight across the moving arm on a set of points. Every few days it would just short out briefly for some reason. I think I found that problem by shotgunning it.
