When overhauling the engine, replacing as many of the wear prone components as possible will simplify the building process and subsequent adjustments required to set up the engine correctly.
The most vital items that require close examination for wear and damage (after the cylinder-head has been sorted) are the components that make up the crankshaft/balance-shaft/piston/cylinder assembly.
This component, and perhaps some of those below maybe required:
Pro-workshop gasket sealant 08C70K0234M to complete the job like a professional! Add as many new parts as you wish, a new piston pin 130021101 and piston pin circlips 920331226 for example, and still only pay the same single fixed price shipping cost. This component may have other applications within the Kawasaki model range - so please ensure the part-number ordered is correct for your application.