I replaced the starter on my 85 300D and found it a little frustrating, however, my recollection is that it was quite straightforward having the tools that made it easier.

You should definitely invest in a set of metric hex sockets (regular 3/8 craftsman, or even the sets I have seen in Auto Zone or Pep Boys seem to be of decent quality). You cant do this work with allen wrenches...and there are a number of other hex socket bolts on this car, so a set of hex sockets is a must.

My recollection on the starter is that there are three hex bolts...the two lower ones are quite easy to remove.

The upper one is the one that can make your hair turn grey...however...I remember using a very long extention bar (24" ?) on my 3/8 rachet with the hex socket on the end. From under the car, I went in with the extention from well behind and above the starter, somewhere up behind near the exhaust header..and I was able to find a very small pathway straight to the starter bolt and I could remove it quite easily. Installation of the new one was quite simple as well. If you try to access that bolt from the immediate vicinity of the starter, it is a real problem.

I bought the long extension several years ago to access upper bell housing bolts when changing clutch on my Toyota Corrola..while I havent used this too much since than, there have been a few instances where it has been a lifesafer.

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)