The LO206 should be a great start for this. The WKA rules are here, hopefully the IKF rules aren’t too different but if they are let me know:
http://worldkarting.com/downloads/Section_705%20Pro%20Gas%20Gold%20Cup.pdf
Of course you will have to change the coil. I would go with a billet rod since the rules allow, and you have to run the spec cam. Other than that it should be a fairly straightforward rebuild.
Just inspect everything else and replace what you have to. It’s supposed to be an economical class I think so I wouldn’t go overboard trying to get the last little bit from the engine.
Good luck and let us know how it works out.
John