From Mercedes Wiki

There have various coachbuilder for W126 models with 1000SEL tag.

SGS: 1000 SGS

Bertone: 1000 SEL

Trasco: 1000 SEL

Kugok: 1000 SEL

Vantagefield: 1000 SEC

Below is the picture of Bertone 1000 SEL which only 3 built for the head of States like Her Highness Maharani Gayatri Devi (Queen Mother of Jaipur), His Majesty Sultan of Brunei and His Serene Higness Albert II, Prince of Monaco.

Bertone Version 1000 SEL