I would replace the coil, coil wire (the one the goes to the distributor cap), the distributor cap, and the rotor. It's cheap and easy to do. If you're not sure of the cap and rotor, pop it off and look for any pitting on the rotor or contacts inside the cap. Also look for any black "tracing" - fine lines around the inside of the rotor. This can indicate that there was arcing, often caused by getting moisture inside the cap, then the cap starts to arc and deposit small amounts of carbon all over the inside of the cap. This creates a conductive trace that can cause all sorts of strange misfires and rough running. It's probably not the source of your problem, but with this particular issue it could bugger up a perfectly good cap as a result.