I don't have much knowledge with the 789x spicer. But if you have the small joint 7260 yoke, I have always used the 315 or 317 (same joint, different grease fitting location) Precision joints with no problem.
^^ You have to keep the rubber grease seals with the caps, and remove the grease Zerk.Then the boss on the u-joint where the seal rides will fit right into one loop allowing the otherside to drop in.
Oops, I guess I shoulda read all the way to the end.