Wow! Great build on a bike made to be motorized.
I think you have room for a 212cc in that frame.
With your bike returned to the stock freewheel,
You will have the same function as a $150 Sick Bike Parts Shift Kit.
This is the great option for top speed for the 79cc.
This guys 79cc is getting 40mph with a SBP shift kit:
4 stoke motorized bicycle 40MPH
You may have problems with the new NC registration and insurance laws.
Thanks for the great hi-res Pics.