My 1980 US spec 450SEL is 100377, so oversize, you have one of the last ones ever made!
As for 6.9's 7380 is the grand total, 1816 for NA e balance for the rest of the world including RHD cars. No 81 cars as far as I know, however I do believe there were a few made in 1980. We have to remember that for certain markets 126's were available as early as late 79 whereas for others 116's soldiered on until about 7/1980
The absolute last 116 was a 300SD.