That head is for a forced air cooled scooter. The only similarities are bolt spacing and the Brand Athena. It would be a horrible idea to put on a passively cooled bike that has shrouding and such in the way. Come to think, really trying to make any significant power will present even more heat issues than other bikes because of the airflow. On that bike, with such a small wheel set and final drive it may be a waste of effort and money to go big for the Athena. Adding an expansion chamber would ruin the purpose of the bike after all.
That ring is for an o-ring, a thin copper wire meant to crush and seal. Not all heads have it.(edited)