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It's seldom productive to start replacing parts without determining the cause of the problem. Often even counterproductive since additional problems can be introduced in the process making it even more difficult to diagnose and solve.
After performing Marshall's test, I'd check for spark at the points. Key on, open and close points with a screwdriver. If no spark, check for a short in the wire between the dizzy plates, bad ignition switch, short or break in wiring to coil or ignition switch.
If spark at points, check for spark at the plugs by disconnecting the spark plug leads and shorting one a quarter inch or so to ground with a screwdriver while cranking the engine key on. If no spark, rotor may be shorting internally.
If spark at plug, check timing.
If timing OK, maybe it's not an electrical problem?