That is a Ponton wagon. It's a Mercedes Chassis and was edited but a company called Binz, which is a Coach Builder. They are truely rare beasts, especially in the US. Binz made a truck on the same chassis.
Here are the Ponton Variants.
http://www.mbzponton.org/pax058/people/photogalleryvariants.htm

What a Mercedes ambulance, hearse, or limo. Check out Binz Coachbuilders - http://www.binzuk.com/index.htm

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