My wife owned a Zephyr 550 in 1998. We raised the rear using the eccentric adjuster (see the image in the Wikipedia article), and replaced the fork springs with progressive units. This had the effect of raising the whole bike evenly, which seemed to work ok.FYI trivia I know Kawasaki GPZ 900R also had a reversible eccentric on the swing arm that would Jack the back up - I never tried it !
Also replaced the rear sprocket with a one tooth smaller item, which reduced the snatchiness at low speeds. Sort of counter-intuitive but it did the job.
