Rookie mechanic: trouble shooting advice requested

Ballast resistors fail no doubt. Ignition modules and magnetic pick ups in distributors are more prone to intermittent come and go type failures. Back when I worked for Ford we would rarely diagnose to determine which of the 2 pieces were at fault. Even when we did know which was the fault ( like a stator melted down ), the customers always got stator and module replaced as a pair. Just good practice to avoid comebacks.