Proper PCV routing?

Hey guys, I have 5.0 HO valve covers (the thick aluminum ones) and I want to make a closed PCV system. Right now I just have an open breather on the one oil filler/pcv thingy.

My question is if I were to cap that off (with the oil cap that comes stock) and route a hose to vacuum, where does air enter the system? the other valve cover has no openings, so where does the air come in?

It can't, unless you make a hole in the valve cover that has no opening.
It will come in wherever it can find a hole.

Well then how do the factory mustangs/lincolns etc. do it? I know they have a closed pcv system.

What car are you doing this to and what type of induction system do you have? Carburetor or fuel injection?

Its a torino and its carbed.

They run to the air cleaner to small filter

You're going to have to cut a hole in the valve cover that does not have the oil cap. Make the hole large enough to put a grommet for a hose in it and make a baffle for it.
Then for the OTHER valve cover, get an oil cap that has the hole in the center for the pcv valve. Run the hose for the pcv valve to the carburetor baseplate and the hose from the other valve cover to the air cleaner.
The reason you want to do it like this is to create a cross-ventilation, drawing the blowby fumes out of the crankcase.