Just because you have a 9" doesn't mean there's one particular U-joint, in fact just for factory 9s I'd bet there's at least 8 of them that are "stock" for a certain application. You not only have the distance between the threaded portion but the OD of the bearing surface as well, also there are some with zerk fittings and some without, some are sealed and some just have the roller-bearings inside. After a few trial and error attempts what I ended up doing was take my parts to the counter and try out several (!!!) until I found one that actually fit, for grins I looked up the part number in the book and according to the book it was for a Mopar application...go figure.
Seriously, as D mentioned, for a universal joint these u-bolts are far from universal....lol.