[Rev]

You may just have the wrong PCV valve. I use the same valve covers that you have. I connect the PCV valve to the right rear valve cover using a rubber grommet with the PCV valve and a hose going to my Road Demon manifold vaccum source. At the front left valve cover, I have cap filled with wire mesh but with a hose connection below that which goes to the air cleaner. That way, there should be some suction to the crank case almost all the time.

I think the rattle may just be due the wrong PCV valve. Get one from a Mustang supply house that's right for the original 289. It should not rattle.

Rev