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I currently have a '84 KZ700. To make a long story short the motor is toast and I cannot find oversize pistons readily. I found a 750 motor from about the same year and I am wondering if the 2 are interchangeable. I know they dropped to a 700 trying to get around additional import taxes, but I find it hard to beleve they redesigned the whole motor. My thinking is they just decreased the bore and maybe the stroke also to lower the displacement. I would think the cases would bolt right into my frame and the clutch and rotor from my old motor wold work. I plan on using a stage 3 kit for the carbs which would give me the aditional fuel needed between larger displacement and 4-1 header. Anyone know for sure on this???

You're correct. Kawaski didn't redesign the engine when it went to 700cc. They just sleeved the cylinders to reduce the bore. The Canadian versions of the bike maintained the original 750cc displacement.

It's been awhile since I worked on one, but I'm about 90% sure that a 750 engine will bolt right in (assuming it's from a similar year). You're best bet on researching this project would be to tap the vast amount of KZ knowledge over at www.kzrider.com You're likely to find a few people who have made that mod, and can tell you if there are any "gotchas".

Good Luck.