First, EGR and PCV are not the same thing.
PCV valve will go in the valve cover.
You may not even have an EGR valve but if you do it would likely be bolted to the intake manifold.
PCV valve in one valve cover will have a hose going to the base of the carburetor.
The other valve cover should have a breather cap as a oil fill cap.
This breather cap should have some sort of filter material inside it. If it doesn’t, then it needs a hose attached to the air cleaner so it gets filtered air.
Bottom line, if your breather cap has a hose attachment, it needs to be connected to the air cleaner.
1970 Mustang coupe