Hello Captain Fantastic, welcome to the site. The frames on the 89 and 88 look fairly similar in pictures. Knowing they were going to the perimeter frame in 1990, I couldn’t imagine Kawasaki making a ton of changes to the motors from 88 to 89. I think it’s worth a try if you can get a deal on the other motor, and you’re comfortable with a little fabrication (in case the motor is a little different).