I bought a used medium extension pin box from our local RV dealer that was a take off when someone bought an aftermarket pin box. Ebay on occasion has one as well.
2020 F250 STX CC SB 7.3L 10spd 3.55 4x4
2010 F250 XLT CC SB 5.4L 5spdTS 3.73
ex '95 Cummins,'98 12v Cummins,'01.5 Cummins,'03 Cummins; '05 Hemi
2017 Jayco 28RLS TT 32.5'