I have one of these tanks in my 300tdi 110. They are great and worth the money. The tank sits under the front drivers seat and with a switch on the dash changes the tank from the rear to the front. At the same time it change the original dash fuel gauge over to the level in the tank you are using at the time.
Only cost $1400 ( about £900).
Here is my 110 , you can see just the tank Under the drivers side.