JTM
I originally decided that I wanted to change the tailight but found that the tailight did not look right and did not want to destroy the original for the same reason as yours so decided to change rear guard using an Airtech smooth bobbed. I used this one as it has the molding to fit up exactly to our bikes.
It is made of fibreglass but I found that it was a bit flimsy so I glassed in some brackets for strength.
I left it longer than the others shown above as I prefer the more classic look but it wouldnt take much to cut the Airtech one down to what you prefer.
Chris