Overhauling the engine will be easier and with a better outcome when all of the wear and damage prone parts are replaced with new, where possible. The bear minimum will be new Piston-rings, lapping the inlet and exhaust valves to ensure a good gas seal and a new cam-chain and tensioner/guide. While the engine is apart ensure the oil pump is in good order, it would be a disaster after an engine rebuild if the oil pump failed!
If the engine requires more attention, then you can stil get most of the parts required here at CMS.
This component, and perhaps some of those listed below, maybe required: