Welcome to the forums Edge!
The ingenuity I see in the Cuban bikes is amazing. I see a kindred spirit in Deacon's creations. From looking at this site: Rikimbili.com
I will venture to guess that the bikes in Cuba go faster because they are often of much larger displacement. Of the authentic Cuban bikes on that site most of them would be much larger than 67cc.
I think the items that would attract the most attention from the authorities would be the Plastic bottle Gas-tanks, The pedal on belt clutch, and the Fred Flinstone brakes!
I hope you enjoy building and riding your Schwinn. Without doubt you will yearn for more speed. Pretty good chance you might find some on this board