Agree with Noobs. I have run both the stock Vertex and Wossner kits. I was really impressed with the wossner. Good quality at the right price point. Freely available from several sources and generally comes with piston, rings, clips, and pin. Throw in a couple base gaskets, little end bearing and you're done.
If you've got a few hours on the bike I'd probably do the head o-rings as a precaution. Also like to have spare water jacket gasket, pv gaskets, exh o rings, and flywheel gasket on hand just incase anything gets torn during pulldown or needs replacing. A smear of grease or gasket goop makes for easy removal next time and better odds of re-using them. Obviously don't bother trying to reuse the base gaskets or head orings (if removed).
Ebay has several kits