Well, by putting in the petronix, you eliminate 2 out of 4 things being bad.

Basically you take out points and the balast being your problem.

The two remaining are the coil and power, which breaks down to two things.

You have key on power in run. That should read 12 volts on one side and around 8 volts on the other of the ballast.

You also have start power which should bypass the ballast and read 12 volts on the coil side when you are turning the key to start the car.

So if you put in the petronix, and the car still doesn't start, then all you have to check is voltage. If there is voltage, then you have a bad coil.

If you try to fix the points, then you have to verify the points aren't burnt out.
That they gap is set correctly, then figure out if the coil or ballast is dead.
Assuming you have voltage at both run and start.