My 84 200 currently has a 96 flywheel with the original 83-4-5 stator coils. I cut a new keyway in the tapered hub once I had the timing sorted due to the magnets being a different offset to the earlier model. The angle took a bit of working out. I eventually got it right by useing a timing light to pinpoint new timing marks then engraving the new timing marks on the flywheel and finally measuring the piston height with a dial gauge to time it.
I didnt even bother having a key in the shaft for about twelve months and never had a problem with it moving on the shaft.
The magnets dont come loose and destroy the coils on the later model flywheel, something that is a real problem on the earlier model flywheels as they get old.
I dont know about the 86-8 model ignition if the same can be acheived with its original coils, but I would asume that changing the entire ignition to a later model might give rise to some problems with advance curves and characteristics of the CDI unit that may not bid well with the earlier air cooled donk.
If I had the parts id try it just to see what happens.
Brian