There is a guy in England that makes adjustable lowering dogbone links (which is the linkage between the swing arm and the rear shock).
I just cannot recall the name of the place right now, but he does have a website where he also sells screens.
I'll keep trying to remember and search for the website.
This isn't a simply job to do though...and, if you lower the rear, then you'll need to lower the front to match (not too hard to do).
A Corbin or Sargant seat can get you about 1 inch too.