Indeed it's going to be a balancing act to get the rim positioned such that you can take measurements. Fortunately the face of the rim is open enough between the spokes that a tape measure can be gotten through! Don't neglect the back end though. While I agree that clearance at the spring seat up front is a much more critical issue, incorrect clearance at the back will have the inside wall of the tires rubbing the inside of the fender well every time you climb a driveway entrance.

As to the height, not unusual. Rim height not usually measured at the outside diameter, but on the seating area inside. My experience is that alloy rims have a wider seat area above the measured point. Perhaps to compensate for the fact that aluminum is not as hard as steel? It certainly takes more stretching to get tires on alloys than on steelies.

DS