AC TMI White Paper: How to Avoid Mousey LWB Turn Signals
As you probably know, lens coloration of turn signals and taillights differed based on the part of the world a Porsche 911 was delivered to in accordance with regulations. Cars delivered to the United States had solid amber turn signals and solid red taillights interrupted by a patch of white for the backup lights. Cars delivered to the rest of the world (RoW, often referred to as Euro) had amber/white turn signal lenses and red/white/amber taillights.
Many prefer the more colorful Euro lenses and simply swap them for the U.S.lenses. That's OK but the housings and bulb mounting pattern is different between the Euro and U.S. lamps.
Dual 21/5w Bulbs
The dual bulbs are mounted behind the amber portion of the lenses, located in the same place on Euro and U.S. turn signals, so we're good there.
4w City Light Bulbs
The 4w city lights were mounted on opposite ends of the Euro vs. the U.S. housings. The Euro version version mounted the bulbs behind the clear area of the lenses, to the medial side of the housing, close to the horn grilles. The U.S. version mounted them on the lateral side where they could also be seen from the side of the car. To accommodate this, the Euro version housings mounted a small bracket to serve as the bulb holders on the medial end of the housing.
The Mousey Part
If you have U.S. housings and prefer to have Euro style lenses, it appears that you can simply swap the lenses as they are the same dimensions. However you will have no bulb behind the clear part of the Euro lens as the 4w bulb will be mounted at the other end, the proper location for U.S. turn signals. If this is how you have things configured and enjoy showing your car, you might reconsider until you fix it. Respectable concours judges will turn pale.
Porsche manufactured a small bracket so the 4w bulb could be mounted at the proper place, the medial end next to the horn grille. Those became pretty much unobtainium over the years and folks fashioned a variety of ways to mount the bulb. AC came across a cache of bare OEM Porsche bulb holders and devised a configuration to mount the bulbs. This is an easy and inexpensive way to use the proper lighting with Euro lenses.
4w City Light Bulbs
You coast downhill here. The only difference between the Euro and U.S. versions is the 4w city light bulbs: the Euro version doesn't have them and the U.S. version does. In your U.S. housings the bulbs are mounted in the large circular reflector mounted at the lateral end of the housing where they can be viewed from the side. In the Euro version there are no reflectors mounted there. Since you're going from U.S. to Euro you can simply leave the bulbs out, or if you prefer strict originality pop the reflectors out.