When You drive these Old Cars an Auto Club Membership or Insurance that has some free Towing and Lock Smithing services is actually a Money Saver in the long run.
If You had the free towing You could have it towed to another Mechanics Shop.
Or if there is parking on the Street You could get a friend and simply Push the Car off the Shops lot and park it on the Street.
My Father and I did that when I was Kid and He had a problem at a Transmission Shop.
As far as the Engine end of the issue goes you need the parts Pictured and the little Nuts for the Glow Plugs.
The 10 Gauge Wires and the Eyes that go in the end can be had at any Auto Parts store and you make Your own wires.
There is a Wire on the Stock Glow Plug System that goes from the Front Glow Plug to the Cylinder Head. With the Adapter Glow Plugs you do not use that Wire; remove it so there is no temptation to connect it.
It is pretty much remove all of the stuff needed to make the Stock Glow Plugs work off of the Engine.
Screw in the Adapter Plugs.
Use the Wires shown in the Pick from one plug to the other and on the Plug near the Fire Wall connect the Wire from the Knob to the Glow Plug.
Again the Adapter Plugs do not need that Ground Wire at the front. The Adapter Plugs are grounded through the Threads just like a Spark Plug is.
I don't know if there is any issues with the Gorilla Knob thing You pull to activate the Glow Plugs.
There is likely info on that at the below site:
DIY Links by Parts Category - PeachParts Mercedes ShopForum
PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles