Originally Posted by Djweaz
Hey John I have been told that it's a one way check valve for the power brake booster which is where the line goes.
That makes more sense. You definitely need to remove that tube on the back of the manifold. You should be able to install a pcv valve without too much difficulty. Your carburetor has a vacuum fitting on the front that will work fine for hooking one up. You can also remove the plug in the back of the carburetor and put a fitting there.