When I hauled trucks out of Janesville ,Wi we had a field with hundreds of little white cabovers.
If a dealer ordered a W4 GMC they went and grabbed one with the proper trans and wb and put GMC badging on it and GMC booklets in it.
If the guy that grabbed that unit had needed an Isuzu or a Chevy,those badges and books would have been installed.
That's all the differance there is between that series of Isuzu,GMC ,and Chevy.