The model differences on the first Gen. were mainly trim packages, as in dipped Camo, raw or painted plastic, steel or aluminum wheels. I think the "sport model" at least some years came with upgraded shocks with compression and rebound adjustment. There are model identification pictures in the front of my 2011 F.S,M. If you are looking at specific parts on PartZilla or Kawasaki.com, you can click on the part# and it will tell which models it fits.
Mike