If you bought the entire 489 "chunk" which is what we call the preassembled unit, it will swap with no problem. You take out the unit with the 276 gears and install the whole unit with the 323s. About the only thing that can be different is the yoke size. As stated already, They make two: a large and a small. You can get a two sided adapter u-joint from a number of locations that is small one side and large on the other.
As noted above a ring and pinion from a 741 case will not fit in a 489 case.
