I had the misfire that you describe, bought new coil and leads, found a good S/H cap at the wreckers.
Pulled the cap and leads off, problem was evident - one of the leads inside the distributor cap had let go of the metal end, and the arcing there had burnt away at the conductor (carbon impregnated fibreglass strands (?)) inside the lead itself. Replaced cap and leads, misfire went away.
If anyone is planning to replace leads, look carefully at how the leads run, and where and how various standoffs are positioned. Don't want a lead to rest on a metal edge and rub through or arc