Cleaning up the 85GT V-6 engine. Can I replace the oil filler cap with a " Crankcase Breather vent/filter , 9mm. WHAT DOES THIS MEAN ???...." it removes the OEM PCV system and relieves pressure. Ebay item from Speed Daddy 4006909975554. Need expert advice from you guys. Thank you.

No. The oil fill cap and PCV valve are different things. You can replace the fresh air intake side of the PCV system with a breather, instead of the valve and tube that connects to the air intake tube (or to the air filter housing, if your car hasn't had the recall work done on it). That part of the PCV system is on the front manifold, not the rear where the oil fill cap is located.