This is the fastest Puch Kit you can get without boring out your stock case to something bigger.
In this Pro Pack, you get a 70cc Athena Kit, and an Amal 15mm carb. That setup alone will work pretty well for you. If you really want to scream though, you need to upgrade to a Dellorto PHBG.
This is a bolt up and go for an E50, but a tad trickier for the ZA50. Some shaving down on the case is necessary to make everything clear.
This comes with metal reeds, either keep an eye on them, or replace them out for some Polini reed paper. Metal reeds don't tend to have a long life.