The 911 headlights are held by the lower screw. You have painted trim rings these are held by a small screw that is screwed in a "hollow" screw.
You can see these screws in this post
http://forums.pelicanparts.com/porsche-911-technical-forum/908301-headlight-trim-ring-screw.html
The headlight assembly ring has two aiming screws and the lower screw .
To disassemble the headlight lens you need to remove some wire clips that hold the lens to the assembly.
The parts you will need :
The lens, the lens gasket, the ring with the adjusting screws, the trim ring and an assembly gasket.
First check who is the manufacturer of your lens, Bosch, Hella, Marelli , AL ? You can see the markings in the other headlight.
I do not see a chrome assembly ring in the Pelican catalog, I only see the p/n you mentioned but it is black not chrome. The black ring you have is the trim ring not the assembly ring.
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