They may be on to something with the coil overheating. You may also want to check the ballast and ignition switch to see how hot they are. I had a similar thing with a dual point, found out inside the distributor was wore out, shorting out the points and condenser which made the whole ignition system to hot.
Have you checked the rotor and cap? How much wear or movement there is inside the distributor ? May want to check the shaft wear and end play as well, also check for broken springs.
Check the HT circuit, make sure you have a good ground from the battery to the block, battery to the radiator support, block to the firewall, coil/condensor to intake, there should be no paint in the threads or under mounting points. Also check to see if you have spark from the center coil wire to the block, if you have a rapid succesion of blue spark, the coil is ok, could be the cap, rotor, points, next check the LT.
Check the low tension circuit with a voltmeter or test bulb and 2 lengths of wire. With the ignition on and the points open, test from + side of the coil to ground. No voltage indicates a break in voltage from the ignition switch, check all the connections from the ignition switch. If there is voltage it means the coil, condenser or there is a broken wire/connection between the coil and distibutor. Take the condenser wire off the points with the points open, test between the moving points and ground, if there is now voltage then the condenser is bad put in a new condenser. If there is still no reading from the moving point to ground, test the (-) side of the coil to ground, if there is a reading (voltage) on the (-) side of the coil to ground, there is a broken wire between the coil and distibutor which needs replaced. If there is no voltage between (-) coil to ground then the coil has failed. Good luck, just some things to check....