Most of the rides have a chair out front that will let you test yourself. However, if alot of his height is in his torso then it will be close. I always test myself since I have a little bit of a gut. Not bad, I have really broad shoulders, 6'3", and wear a 3xl. They have special seats on almost all their rides for people a little bigger than the rest. I am thinking he will have problems at 6'10" unless quite a bit of his height is in his legs. I never really had more than 2" of clearance above my shoulders. Hard to know for sure since I was not watching closely to the harness to see if it lowered in addition to moving the harness on your chest. I had an extreme concern about the forbidden journey ride since I heard it was anti-fat people. (They put in new harnesses by the way in November) I called the Universal disabilities number since I thought above anyone else they would know the weight and height restrictions on the rides. They were really friendly and I was safe. I would call first since Universal is expensive. $115 for a one day multipark ticket in addition to parking or taxi service to get there.