CUDA DIED...NO SPARK to PLUGS !!

1st the ballast; single or dual, check for open circuit with key in run position & start position.
2nd is the rotor turning during cranking- on a /6 the dist. gear may be broken, on V8's it could be the timing chain.
3rd ignition box, not the most likely failure, but easy to diagnose with a known good unit.
4th distributor pick up, in my experience it's the 2nd most common failure item after the resistor, but more of a PIA to replace.