360 motor loses ignition when warm

I have a small block 360 motor in a '69 Valiant. It fires up immediately when starting cold but a few days ago out cruising the motor died after warming up. It would crank but not start. Very weak spark. After waiting two hours for it to cool down, started right up and died again after running five minutes until warm. Then it just turns over with nothing-no hiccups, rough running, nothing. I can start it all day long (cold motor) but when the motor gets hot it dies. Any suggestions? ballast? coil? One person said it was a heat sink in the distributor...no points, Mopar orange box electronic ignition....HELP!