Intermittent shutting off issue

Hi! Please help! Intermittent ignition problem for months now and have tried practically everything I know. I rebuilt with 1978 and 1983 parts 15 years ago. There’s a lot of stuff on the wiring harness that’s not connected. So, it would just turn off while running. Not stall, it’s definitely getting gas, but turn off. Some times it would turn back on before I could even get off to the side of the road. Some times it wouldn’t start for hours. Some times I would haul it back to the house and it would start as soon as I got it off the trailer. No correlation to speed or amount of time driven (warmth of engine). Started with the ignition switch, still had a problem. Then I replaced the ICM, still had a problem. I have now replaced the distributor, spark plug wires and the coil. They’re 40+ years old anyway so I wasn’t concerned about replacing parts I don’t need. After installing the new coil it still won’t turn over. I have 12v to the positive terminal wire that connects to the coil until it is connected then it’s only 6.5v. I have 6.5v then also transferring into the distributor. Help!