This is probably something you'll have to figure out for yourself. A KZ305 or 440 tank probably won't be a direct bolt-on. I would guess that your best bet would be an 80s KZ250-Ltd or -CSR tank. Search ebbaayy for KZ250 tank - several are listed & they look similar to the one in the diagrams at Kawasaki.com. Your tank has a distinctive rear mounting hook that's kinda unusual (to me anyway), but it helps in identifying a potential match. Comparing the KZ250 fuel tank part numbers from the various years might shed some light as to what might fit.
