You really don't want to get into swapping field coils. It's a royal pain in the butt and takes a dedicated "pole shoe vise" to hold the socket or drag link tool tight enough into the bolt that attaches the pole shoe to the housing to keep from stripping it out. Unless there's an oldtime electrical rebuilder in your neighborhood, it's unlikely anyone around the parts supply business has ever seen one. IF you managed to change the field coils, you're only halfway there. You would still need a 12 volt armature.
Does the generator on your 8N have the oddball front housing that also mounts the fan pivot, or is it mounted off to one side like a normal generator? If it's an offset mount type, just get a 1956 Ford 12 volt generatorand bolt it on. It's the only 12 volt Ford that's set up for positive ground. Use the right regulator, and you'll have a stock-appearing system with the right voltage and polarity to run 12 volts. If you want to run 12V negative ground so you can still use the Pertronix (can't imagine why you would) just use a 1957-61 Ford generator and a negative ground regulator.
Jerry
