The threaded opening into the #4 runner is for the power brakes. If manu8al brakes, leave it plugged. If power, get a brass elbow with 3/8" hose on one end, 3/8 pipe on the other.
PCV goes onto 3/8" hose at base of carb. This way,
oil vapors and additional air get distributed evenly to all cylinders. You can see how getting this backwards would have all the
oil vapors and extra air going only to #4 cylinder. "T" won't work either as it reduces the vacuum available to power booster by the air drawn if through the PCV.