yup cb650 motor drops right in, but the wiring and ignition is gonna be a little trickier if the 650 has electronic ignition. I wouldn't mind finding a 650 for my 550 myself. I don't think there is much point in a 550 owner wasting precious time/money/garage space on a 360. I rode one for a few years before I got my first sohc4, and there really isn't much to compare. If you want a six speed, find yourself a 400 4. Few people were beating down my door to buy my clean, original, under 15000 mile cb360 for $900. Granted, jap bikes are generally cheap here in Michigan, and the market has changed a bit since I sold it 5 years ago.