I would say yes you should order for an 89, however if you had a better picture of the motor it would be easier to identify, when you have the exhaust off look inside, if there is a center KIPS valve in the exhaust port defineately 89 or newer. by the way the piston will work whether it is an 88 or 89, gaskets would be different though. 89 had a standard thick head gasket, and it was really expensive, they also offered an optional thin gasket, go for the thin gasket, bumps up compression a bit.
when you say replate the cylinder I'm assuming it is shot, if not your throwing your money away. Kaw rider is offering $180 replates, can't beat the price