Adding more length by extending the pin box or raising the pin location with a goose neck adapter increases the moment arm seen the the frame at the pin attachment point. The frame is designed to carry normal loads, not the excessive loads created by increasing the length of the pinbox. if you are an engineer, it is pretty easy to look at the forces on the pin and surrounding frame.
I have seen two 5ers with frame damage due to the use of a GN adapter. Not cheap to repair.
Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot