From the video link provided, it appears the fiberglass area
between the 2X bulb housings needs to be removed.
Also the lower taillight cutout needs to be partially filled+painted.
Video shows whole process but is in French, so best of luck with that.
If you don't want to mess with it yourself, just find a competent fiberglass bodyman. It'll be a piece of cake for him. Then, I'd recommend going with LED rectangular lights. Mine look original, until I hit the brakes, and then, they'll definitely get someone's attention.
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Karlos
"In the Land of the Pigs, The Butcher is King"