I was going to say that seat looks like a re-covered Corbin, but the back is way too high. Take the seat off and see if it's stock Honda or Corbin. The seat release is on the right side where you see the keylock but the grab bar above the shock.
I really like the Corbin seats vs the stock ones, the stock ones look too flat and are know for less comfort than the Corbin. The problem is the Corbin seat is big $$. I recovered my stock one before I bought a bike that had the Corbin already on it. When I recovered mine, I used a hack saw blade to custom trim the driver seat area. I made it look more corbin like. Then used $10 worth of vinal and warmed/pulled stapled it into place. Looked good, was cheap, but then I got the corbin (which has a tear in it, so it's up for recover next)
Nice looking bike, congrats on a great classic! Might want to keep your eyes open for some case guards, I got a set from my parts bike and they saved my bike when it went down.
I'd start with some soapy water and wet sand at about 1500 grit. Use light pressure and that should remove that outer layer of oxidized plastic. Then rubbing compound, then polish. Don't heat it up with a power polisher by staying too long in one spot.
Here's a pic of my Corbin seat, notice it sits about even with the rear grab bar (second pic shows what one style of crash bars look like):
http://nighthawk-forums.com/index.php/topic,11005.0.html
