It should be said again that the rack dampener bolt on the rear of the IP on most of these has been changed to a gold colored bolt by now. There are still some out there that are to old steel color and they should be replaced with the upgraded gold toned.
I have an 81 SD and had a similar shake with the car at one time. There is no magic bullet with most of these to get a smooth idle, but if you are persistant you can sort the problems out and get it to idle smoothly.
First thing is that rack dampener bolt. Pull it out and check the color. If is is plain steel color then order a new one and install it. To adjust the fuel rack dampener you should turn that bolt in incrementally with the engine fully warmed. As it turns in you may see the idle shake reduced. If turned in too far when you rev the engine it will stumble. If after setting it you notice the engine dies when yo bring it to a stop, then turn the bolt out a little. Takes a 14 mm and 12 mm wrench to get the bolt a lock nut tightened.
Next is the valve adjustment and timing chain. There are lots of threads on the best way to do the valves. I found the Haynes Mercedes Diesel manual has an excellent section on the valve settings
Check the timing chain stretch while you are in there. Again there has been some great threads on this. Search for them. I replaced the timing chain earlier this year and was rewarded with a smoother idle on my older 78 300D.
After that if you still have a peristantly rough idle, then it is time to check the start of delivery timing. Not a bad DIY job at all. You will need the drip tube, but it is not that expensive. The Haynes Mercedes manuel has some very good instructions for that also.
Lastly the injectors can need attention. I just took mine into a local diesel injector service and had them rebuilt. Some have had success here dismantling them and cleaning them.
While you are at it run a compression test on the engine. A difference in compression between the cylinders may cause a rough idle.
Good luck, and take your time. This can be a great learning experience.