I believe there are two designs of the plastic air boxes. One has provisions for air tubes and a metal elbow oil breather which were not used on the 914-6. Some 911 models have the oil breather pointing the opposite direction as well.
The other is all plastic including the breather elbow and no extra provisions for air tubes.
The other thing that is really hard to find is the air intake trumpet with no provision for the preheat hose. The 914-6 and early 911's ran this type.
I have been researching this topic and have seen lots of factory 914-6's with all types of air boxes. Metal, plastic, with and with out hose hook up, snorkel pointing right, snorkel pointing left...yadda...yadda.
The Porsche PET shows a diagram of a air box with out any provision for any auxiliary air hook ups. It also shows the carburetor spring clip mounts having the solid clips vs the wire type. But it is just a drawing. I have no clue which is correct for the factory 914-6 ?