Your engine is actually GY6 variant.
The GY6 was an engine developed by honda during the 80s, as such you actually have a lot of options, when shop look for GY6 parts.
GY6 Wikipedia Info CLICK HERE
The kawasaki curve has a lot of racing parts, you can actually convert it to 4 valves. It is compatible with the Kymco Jockey Big valve head... 4valves