NA valve cover vent hoses? Which one?

Mazda parts catalog shows two part numbers for the 90, b61P-13-742A and b61P-13-742C.  No indication about vin cutoff numbers,etc.  The one that came off the car has a little restrictor in it.  The replacement didn't (I picked up the 742A version, not realizing that there were two different flavors).

Is the restrictor necessary?

PCV valve?

No, the one that goes from the chrome pipe to the driver's side of the valve cover.

No, the one that goes from the chrome pipe to the driver's side of the valve cover.

Walked out and pinched same hose, doesn't seem to be anything except hose.

Hmmm..., I'm not aware of a restrictor/orifice either, but perhaps it was added to reduce the amount of oil getting through the tube?

Digging up an old thread because I finally solved it.  According to the parts schematic for a 1990, there's a little plastic orifice (with its own separate part number) that goes inside that tube.  It has a singular orientation, not sure what happens without it.  It's reusable in the event that you have to replace the rubber line, as I had to when the original one cracked.

I can't tell you how many times I've looked at this schematic and never saw the orifice until recently.  Eureka!