8 3/4s didn't get stamped with any #s like the engine/trans did. The 8 3/4 used paint stamps and paint markings on the housing and center section. If the housing has been blasted and painted before(or if it's super rusty) those paint marks are gone. You can soak the housing and center section in a rust removing product like EvapoRust. It will remove the rust and leave behind any leftover paint. You might get lucky and still see the factory markings.