I like your speedo and the neccessary work sounds not to be very difficult.
Btw.:
Don't worry your English, I think it's almost perfect - anyway, it meets the skills of most of us...
Your German skills will be helpfull too.
Welcome to gs-500.de, have fun!
Edit: I'm looking forward to read more about your planed modifications as well as pics while working on it and, of course, of a hopefully finished custom GS.