Hey Frontman,
I don't know about the 8N specifically but in general when you reverse polarity in a DC system you will cook anything that is dependent on a negative (or positive) ground , such as start motors, coils, etc. since they are dependent on the flow of electrons from only one direction. (Starter motors because power flowing the wrong way will run it in reverse) And the alternator, could be effected as its a similar to a electric motor and power flowing in the wrong direction might cause it to cook the internal wire windings as it fights to turn
As for the fuses, they blow when the power traveling over the filament is more than its rated for.
So if the motor cranks but you get no spark, I would check the ignition coil and see if it looks cooked. If its an electronic ignition, then I would bet that it's done for. The alternator would be the place I would look if the battery failed to charge or ran down after running it for a while.
HTH