If I were you I would call up Paxton or Vortech and find someone near you who does custom work on foriegn cars. You can have a American made supercharger installed for a lot less. I have looked into adding a supercharger to a 300E and it is not that hard. Easily tied into the factory serpentine belt system.
I estimated the cost to be under $3500 on the high side.(Supercharger, Intercooler, Exhaust & Modifications.)

I have never installed a supercharger on a 300E but have installed turbos. I have installed Supers on Fords, VWs, BMWs, Toyotas and many other cars. Adding the supercharger to the 300E would be just as easy as installing one on a 190E. (a lot of room!)

The picture below is a customers car that I installed a Paxton on.
Total cost was $2600. Car is a 1991 318i 4 cylinder. Power output is 215HP @ 9psi., not bad for a 4 cyl.

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WARNING: Bastard Mercedes Builder/Tuner
Sorry if I don't answer your email or questions
I don't check here too often.
I am normally on the 190revolution.net board.
Thanks