there are a few limitations due to the design of the bike.
The tank is long, so clip-ons end up giving you a little too much reach forward that certainly isn't optimal with the footpegs being where they are.
In terms of lower and narrower handlebars, you're pretty limited by the tank in terms of how low and narrow you can go, it doesn't take long before your bars are hitting the tank.
Best compromise I've found is (like beetle) running Laverda Jota bars. These can be adjusted agreat deal. I have mine installed with no risers and they only just clear the tank, gives me a nice position and I haven't had to change any cables.
In fact if guzzi had just put a decent seat on this thing, I'd say my bike now has a near perfect riding position. Sat on my friends K1300S the other day and just couldn't believe how much better the BMW seat is.