Definitely train him as a guard if you want him on the U21 team. He will never land a SF spot with atrocious inside shot and pitiful rebounding. As for how to train him. I would keep jacking up the OD and passing because they are usually the most important to U21 NT coaches. After that just train 1v1 for guards.
Murray/Harris/MPJ/Grant/Jokic - 2020 NBA Champs