Even with a 12V system, my old Ford Jubilee would often have condensation problems allowing the spark to jump to ground long before it made it's way up the wires to the plugs. If you have electricity nearby, a hair dryer inside the distributor could work wonders. Also, make sure the coil and distributor cap are very clean/dry inside and outside. Pull the plug wires and clean off the plug insulators too. Clean and dry really makes a difference on old 6V and even 12V systems.
When I was experiencing problems with my system, I would always check that I had power to the coil when the key was turned on. A voltmeter or test lamp can show that quickly. Next, I'd pull the wire from the coil off the distributor cap and remove the distributor cap. Then, while holding the coil wire end very close to ground, I'd open and close the points manually to create a spark from the end of the coil wire (if you aren't careful, you'll get a jolt too). Of course, the engine/rotor has to be turned so the points are closed to start with, but that's easy to do by tugging on the fan belt or using the starter motor. You can watch the points to see that they open and close as they ride on the distributor cam face. While they are open, you should be able to measure the 6 volts from the coil. If you don't get a spark jumping from the coil wire when you open the points, then they need attention/cleaning/adjusting. By doing this test, you can check out everything except the rotor and high voltage distributor cap functions. Normally the rotor and cap will work fine if dry and carefully seated in the proper position.
Since you say that your 8N runs great once it starts, I'd be that if you get everything clean and dry, you won't even have to do the "experiments" above.