I would check that spark plug wire carefully (I would test all of them while your at it ) with a Volt Ohm meter and twist both ends, spark plug and distributor ends, to see if it is going bad (varying ohm readings)
I've had several wires go bad at the 90 degree distributor ends, the nylon that is graphite coated had all the graphite burnt off of them
I cut around one inch off of each one of the bad ones to get back to some good looking inner conductor and race that car some more
IHTHs