64 Plymouth 273 Intermitent severe misfire.

Do you have a tach/ dwell meter? Some of those have a points resistance scale. So check the points for condition. If you don't have one, Turn the key to "run" and check coil+ voltage. If it is full battery voltage the points are open. Bump the engine until the coil+ voltage drops. It should read about 6-10V or so. While you are at this, wiggle the bulkhead connector and see if the voltage drops badly.

Next measure coil NEG voltage. It should be less than 1 volt, better if less than 1/2 volt. This gives you some idea of points resistance. The higher this reading, the worse the points condition is

Do this as quickly as you can, you don't want to leave the key on very long with engine stopped. If you are in the habit of doing so, you may have damaged the points

Condensers are an "iffy" thing and modern Chineseoationized replacements are not particularly reliable

Next check spark. "Rig" a gap/ modified plug/ spark gap/ tester with a SOLID coil wire where you can see it. Crank the engine USING THE KEY. Do not jumper the starter relay for this test. The spark should be snappy and blue, and jump at least 3/8" and typically 1/2"

Check distributor for shaft play and stuck advance weights.

IF YOU DO NOT HAVE ONE wander over to MyMopar and download a free service manual.

If the timing seems reasonable, I'd start checking fuel. Get a pressure/ vacuum gauge, all real parts stores have them and they are not too much. You can check fuel pump pressure AND volume (read the service manual, chapter 9 I think) anyway fuel section.

Pull the plugs and post photo(s) of them