Ignition coils normally don't explode, but if you're running 12v through any automotive coil for prolonged periods of time and if your points are closed, that's a recipe for trouble. Automotive coils weren't designed for this. They're all about a low voltage primary winding (which when energized will instantly form a magnetic field around the coil), a secondary winding (which when surrounded by this field will produce the high voltage needed for your spark plugs) and the collapse/restoration of that primary magnetic field which is regulated by the points and the condenser...and this happens very fast. Fractions of a second fast, even in a 216. The high voltage energy travels through the rotor/dist cap and coil and spark plug wires and is transmitted to each cylinder when needed to complete the combustion process. The ballast resistor keeps a 12v coil limited to somewhere between 7 and 9 volts (depending entirely on who made the resistor). It lets your coil stay cooler, last longer and operate more efficiently. In basic terms, I think that's about it, however it does get much more complex the deeper into the forest you go. Jerry and about a half dozen people on this forum can take you there, but with a 216 I don't think you need to spend too much time on it.
In your case "Flamethrower" seems to be an apt name for another Pertronix mess. Very glad you weren't standing next to it when it failed and did its flamethrowing. Definitely use a ballast resistor and definitely try to find a more stable coil. As far as I know, MSD coils are still made in the USA, but that's the only one I'm aware of that still is (or may be). You could probably find a decent old or maybe NOS coil on eBay. Good luck!
