I was able to fit an Airhead in my Vega. It is a tight fit, and Rick is right, a tall guy does have to bend a little (not bad, just the head). The width and depth is fine, but the Airhead is 19 inches tall.
By the way, this head uses a very flexible hose for the vent (it ships with 7 feet). However 1.5 inch PVC pipe fittings fit the hose just fine. When I needed a little more length I want to a swimming pools supply store and bought some flexible PVC -- much cheaper and works great.
One thing I am trying to do it to vent it at the stern. I talked with the owner of Airhead and he said he has vented over 20 feet. My biggest problem is that the vent hose shouldn't sag as it will collect moisture. Not sure if it will be possible or not.