Not sure if Salem-Kroger is doing conversions any more - but one of the guys there is doing them now at his own company:
http://whitefeatherconversions.com/home
Here is what their website says...
Whitefeather Conversions is committed to engineering and building the best 4x4 and 6x6 conversions, this is not a sideline to some other business, this is our only business. We are the only production 4x4 Sprinter converter in North America. Whitefeather builds with all new, all top quality parts. One of Whitefeather’s owners and founders, Craig Jackson (formerly engineer at Salem Kroger 4X4) has over 25 years of 4x4 conversion engineering and design with over 3,000 civilian, government and military vehicles shipped to 46 countries including Sprinters to North America, Africa and Europe starting in 2007. The Euro Sprinter 4x4 conversions do not meet strict American D.O.T. safety standards, ours are certified US D.O.T. legal and are able to be exported. The Whitefeather conversion does not void your Mercedes warranty and we cover all of our work with a 3 year 36,000 mile parts and labor limited warranty good world wide, our warranty even includes ambulances and military vehicles.