It's not just the Bay Star and Bay Star Sport...
The Canyon Star line (giants at up to 39'11" overall) use the top of the line 26,000lb GVWR for all floorplans in:
*Non-OEM wheelbases of 220", 260", and 266" and
*Two using the OEM 242"
As I understand, Ford has certified several makers to make substantial changes to the chassis, while maintaining structure and warranty. And driveshaft balance is a big part of that modification.
Maybe someone has seen the process on the factory tour to know if it is a stretch or bob (?).