I just bought a new truck that had goosneck in it and bought the Andersen hitch and got the new aluminum one, I have not been able to use it yet but looks pretty easy, they do have a different hitch that is made for truck with flatbed trucks.
3221 - Aluminum Ultimate 5th Wheel Connection–Gooseneck version (lowered) NOTE: This unit is 4" lower than the standard 3220 and is intended to be used with flatbed or super-lifted trucks that have a RECESSED gooseneck ball. If your gooseneck ball is not recessed, please see part #3220.