w116 350se transmission identiy

[Silver Boat]

I have a 1976 Euro 350se with an automatic trasmission. I beleive it is a 4 speed, but the library on the w116.org states it is a three speed. Where is the trasmission number so that I can verify that I ordered the correct tras filter for my upcomming filter and fluid change. Also how much fluid should it take? I plan on draining the torq converter as well. I figure I will use Mobil One, but I may use some cheap stuff and drive it around for a few weeks and then do it again as the fluid is fairly dark, not black but a brownish red. I know you cannot get out all of the fluid without a compleate teardown.