Presuming the plugs are in good shape & they get healthy spark when grounded to the cylinder/head then my bet is on the R/R.
You might also want to test the coils per the Haynes manual.
The ignition sensor a/k/a pick-up coil is another possibility, however they don't normally fail in the manner of your bike's symptoms.
If you can at least temporarily try a known good R/R then you can rule it out...if you buy one and that is not the problem then it can be sold pretty easily, as the OEM R/R is a common failure/weak point, at least on the carb bikes.
