I can tell you that i spent just as long researching it and searching.
Without a doubt the best thing I did was a head kit,
For the price they are selling that one for it would be a great upgrade.
There is another one which is a 3d port headkit with 15:1 compression ratio.
This option will work for you too
Ozminimoto - Mini Pocket Bikes - Product Detail
I wasn't able to fit a fatboy exhaust on my cag because of the frame design but if you did buy a fatboy exhaust, and a headkit your bike will go great.
The good thing about the ebay one you found was that it has a full circle crank in as well.
The standard clutches are ok, you will just want to get stronger springs for it.
Just a set of fibreglass reeds will do great. Others use polini reeds modified to fit, but its up to you how much you want to do yourself
