For what it is worth, I am one of the two 5.0 owners who punches holes in their beds because of clearance issues. My truck was a 2010 Chevy Silverado. The other was a 2010 Ford F150. Our trucks measure 54" at the top of the rail at the rear most point on the bed rail. If you drive a full size pickup, I would be very cautious about having anything mounted above the existing bed rail...
Jackie and Pam Erikson
2016 Ford F-150 SuperCrew EcoBoost
2015 5.0TA "Texas Style"
2005 Border Collie - "Guinness"