ford 9"

Hello everyone,
My 69 dart came with a fud 9" rear when I bought it. The previous owners work was complete butchery. My questions are what is proper way to change to a 9" so I can go behind this guy and correct any shortcuts he might have done. Also should I even keep the 9", it has some pinion bearing noise and growls slightly at coast, so before I tear into it, I want to decide if I even want to keep it. thanks.