The sector shaft connects to the pitman arm. There are two sizes which are grouped into "large" and "small". Most factory manual boxes are small sector with exceptions such a C-bodies and Vans. Power steering up to 72 was small sector, 73 and later was large sector.
Here is a link to more info:
steering sector
If you have a small sector now and the steering box turns out to be large sector, then that could be a problem depending on the year of the car. You can't easily use a 73 and up power steering pitman arm on a pre-73 because Mopar changed the orientation of the ball joint end. Early ones had the threads pointing up, later ones had the threads pointing down.
Here is more info on
pitman arms
