I wouldn't worry as much about the pin hgt as I would about the actual overhang on the front. Thats where you need to have at least 6" of clearance with your bed rails on the truck. A normal 5th wheel will drop your truck be around 2"+/-. I would measure the bed rails empty, then minus 2" and use that as a gauge when shopping. 5th wheel pin boxes can usually be moved up or down a set of holes which could give you 2" either way. The 5th hitch also has vertical adjustments.
Another thing is not all 5th hitches have the same height settings. Some start higher than others. Like 14" at the lowest to say 16" at the lowest.