Is the turbo in this model the same as in the 300SDL and if so, would it be the Garrett T3 or some other designation? Also I'm having a hard time finding instructions to R&R this turbo.

 

Unfortunately I do not have a DIY on the R&R for the turbo; but I have attached our W126 DIY directory for you below. It should be a helpful guide for you in the future if doing any repairs or maintenance. Best of luck!

Mercedes-Benz S-Class W126 (1981-1991) Technical Articles - Pelican Parts