To install the gas tank cap seal I used another 3M product designed for seals and gaskets. It dries super fast and does a great job.
Things really came together on the bike last night. The headset is on and all the wiring is labeled. One recommendation I have for running the clutch and front break cables is to remove the inner cables and run them down starting from the headset. It's much easier that way. Pictured below you'll see blue painter's tape over the Vespa emblem, which holds it down flush to the frame while the 3M Adhesive dries.
Here's the next HOT items to tackle:
1) Determine why the gas tap flows so poorly and replace if needed.
2) Connect the electrical.