A Timken rear will not fit in a housing built for a Corporate rear, but Timken and Eaton both built housings for both and wheel ends could be specced. This GMC has
a vacuum shift Timken.

https://photos.app.goo.gl/xmKDnJBj2vBgPTFe7

I was a licensed salvage dealer for many years. Trucks don't always have what came from the factory and two tons could be specced with various componants.
Sometimes you have to just take them apart and see what you have.

https://photos.app.goo.gl/EDNt6enVJkfzCpTL6