The line that does go back to the fuel tank . It is your air supply to the tank , so you don't create a vacuum in the tank as the fuel is used . If you don't filter the air going in , the crud will end up in the tank or clogging the line. Same with the over flow vents on the carbs , if you sink a float then the fuel will dump on the hot header . As to the valve cover filter most likely you will be smelling the blow by in the cabin of the car . The little filter will catch the oil particules but the smell will vent in the engine bay.

On the line that goes back to the fuel tank, is it a vacuum line? Does it need to be connected to an existing vacuum line? Or does it just need to be filtered?

Thanks again...Robert

Marty, I don't know the part number. I bought from my Z mechanic.