TO TROUBLESHOOT THIS
Start by "rigging" something to form a test spark gap or buy one. "Rig" this to the coil tower using solid core wire, not the resistor spark plug wire probably used. If the wire to the test gap is kept away from other metal, it can even be a bare or low voltage wire. Crank the engine USING THE KEY that is do not jumper the starter relay. The coil should generate a nice hot blue spark, at least 3/8" long and likely longer
If not, measure coil + voltage with the key in the "run" position. If it is about 8--10V it is OK for now. If it is "same as battery" the points are open. "Bump" the engine until the points close and recheck
Check starting voltage, again at coil + while cranking the engine using the key. Voltage should be very close to "same as battery." Now measure directly at battery while cranking to get that reference figure. Both voltage readings should be at least 10.5V or more
Maybe the points are burned and have high resistance. Turn the key to run, measure coil NEG voltage. should not be more than 1 volt at most. If it is "same as battery" the points are open, bump the engine
The remaining possibilities, if the above all checks out, is coil going bad or bad distributor capacitor (condenser)
Also check the distributor shaft for excessive wear, general condition of points, rubbing block, a tiny bit of points/ cam lube
It also might be that the points are not getting a good ground. This is especially troublesome on dual point distributors, because the advance plate rides on a bearing, and there must be a small flexible ground braid, which can break or come loose.
There is no good way to check either a capacitor (condenser) or coil without special equipment. If the points and voltage checks out, replace the cap because it is cheap. If that doesn't cure it try a coil. It does not hurt to have a spare coil, in any case.
I'm going TO REPEAT one of the first steps. DO NOT use the coil wire to check spark, as they are usually resistive and can lead you down the wrong road.