Going back to Chrysler ignition

The only 300 ohm coils I've seen in ignition context have been magnetic pick-up coils. I'm not sure what ignition coil you are running, but to run it without a ballast resistor is likely to mean you are either overheating it or have a coil with so much internal current limiting that it won't build up much of a spark. If you're using a standard Mopar box, you will need a ballast resistor and a coil designed for one. Otherwise, as the Dread Pirate Roberts put it, "Get used to disappointment."

And it is not uncommon for different ignition boxes to have slightly different timing, so I would get out the timing light once you have the right coil.