Looking through the FAM (see attached) there is one unique part for the 5000 Series trucks. This is #3703694 the mount bracket to the sub frame. All of the other parts are interchangeable with all models.
https://www.flickr.com/photos/advance-design_parts_co/14302025531/in/set-72157631868452754
This shows a typical 3000-4000-6000 bracket (3100 has a special off-set bracket on the frame side, other is the common #3690029) everything else here will work including shims and anchor nut plate. It would appear the sub frame bracket is a sheet stamped assembly to fit into the unique COE cross frame member. As such it may be fairly easy to fabricate a suitable replacement and then use the parts from the standard cab for the rest.
https://www.flickr.com/photos/advance-design_parts_co/8129510232/in/set-72157631868452754