Start diagnosis in reverse order of ignition system from spark plug, plug wires, distributor, distributor cap, rotor, ignitor wire and ignition coil. Whole testing will take 15 minutes maximum.
Additionally, install a relay on ignition coil. It's going to make it better overall aside from this issue.
For now, with engine running in complete dark, spray some water on plug wires, distributor, distributor cap, ignition coil (a little bit). Use water sprayer and don't throw a bucket of water. Lol. Do you see any small sparks anywhere?