On the more modern power steering pumps, the "orifice" is in a screw-in fitting near where the pressure line screws into it on the back of the pump. If the orifice is too large, it can cause an overboost situation where the wheel will turn if you breathe on it the wrong way. It's the size of the orifice that determines the amount of boost the system has. On the Saginaw pumps, there were basically two diameter orifices--one for cars and one for light trucks, with the cars having the larger/higher boost orifices, at least back in the 1960s, and the heavier cars probably having a slightly larger one than the lower level and lighter weight vehicles. Just a few thousanths of an inch difference in the hole diameter can make a bigger difference than you might suspect.
The distance of the orifice from the pump may well have something to do with reducing a harmonic caused by the fluid flow in the hose, so making sure all of the dimensions are "dead on" from the production hose is important.
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