The M has screwed on tank rubbers, L has them glued on.
The rear subframe of the M is wider than the L. Seat units and plastics are also different and won't fit without modification. Also the M has an extra brace under the battery box.
AFAIK those are the only differences.
The N is the same bike as the M but with a different paintjob. Some might say a better paintjob. The real world got the WN in '92.