I had no idea that there was a 600 with M100.985. It has 3 speed transmission too!
Just found this photo gallery https://www.oldtimer-hollen.sk/sk/Renovacie/Prebiehajuce/Mercedes-Benz-600.alej
Was this a MB made 6.9 or is it a custom project?
600 #796 (1967 US version)
300SEL 6.3 #1285 (1969 EURO version)
300SEL 6.3 #5346 (1971 US version project)