response has none, sunsetter i think you can get 900, but am not positive. I know my old sunsetter had 500, but i think you can get rear tanks in the new one.
The reason it's complicated to say how much weight the MLS system adds on a "Sunsetter" is because Malibu has had many Sunsetter models in the line over the year. In 2002 there was the Sunsetter LXi and standard Sunsetter, both of which had a purported 500 lbs. of ballast from the stock MLS system (it's probably closer to 400 though). That's standard on any direct drive Sunsetter.