If your 28 has the wiring block change/mod, the ammeter should wiggle with the ignition on and turning the motor over via the starter. This tells you the primary wiring/coil primary/points are working. Or take the cap and rotor off, ignition on, turn the motor over with the starter, should see a spark at the points contacts. Check your ignition connections and clean your points.
Disconnect the coil/dist. wire at the dist., lay the free end next to unpainted stud nut, turn the engine over and you should get a spark. This tells you have good secondary. Then do the same with a plug lead. Take the lead off and place close to where it should go, tells you the secondary dist. components are OK.
Do you have the Nurex dist. modern plates set up? If yes they can be troublesome and symptoms are varied and strange.
If points not sparking, disconnect condenser, it may be shorting.
There is more depending on what your results are. gets you started. good luck.