We have converted 7 Hustler Super Z 60" with the Kawasaki FX850 and 1 Wright Stander rapid height 36" with the Kawasaki FS600. We have seen an incredible amount of fuel savings. The oil after 100 hours looks almost like new. Oil still needs to be changed though because of the heat breaking it down. We went with Metro Lawn Conversions (A division of Amerigas). You can talk to your dealer about them getting setup so you have somewhere to go to for service or Metro Lawn may work with you as well. The kits consist of replacing the carb with a lp throttle body, installing a regulator and then mounting the tanks. Very simple install using Metro Lawn Conversions.
Check out this link for a fuel savings calculator: