I suspect 2 things. The resistor wire is intermittently screwing up after things get warmed up/hot. Is the coil wired properly? You need not go the HEI route necessarily. Try this site: www.pertronix.com This system converts your already-existing didtributor to a solid state electronic ignition. Once on the site, click on “Ignition”, then “Ignitor”. I use this system in my '71 Chevy van, 250 c.i./ L-6. It has worked without fault for ten years. It’s a simple swap-out of the points for a small module that uses the same existing hold-down screws and works on the Hall Effect-type of ignition. Better, quicker starts, completely reliable in all temperatures/weather conditions in the middle of the Colorado Rockies, etc. My original point set-up was eating points about every 300-500 miles. Removed the part of the resistor wire that does the resistance work. Replaced it with a ceramic block-type resistor mounted on the firewall with one large sheet metal screw. Mine happens to be a Chrysler block resistor matched closely to what Chevy says should be the resistance specifications. I believe that Americam Motors block resistors would work, also. Perhaps a Ford-type resistor block? End of points burning up. But I got sick and tired of bending over the didtributor to re-adjust the points every 10K miles or so and installed the Pertronix system. Better starts, better performance, no more occasional backfires due to the vacuum advance, etc.