Turbo kits for our cars are expensive, unless home fabricated, because there isn't as high a demand. Check out mercedesshop.com for home turbo fabrication tips. Since you're already running a small version of the m103 an easy thing is switching your engine with one from a 300e (12valve), or an m104 (24vlv). There's a picture of one on the tripod site of the 24vlv conversion, the only problem is there's no room for a turbo. There's also a picture of a C36 hybrid on that site. The 12vlv leaves room for a turbo. AMG put out a 6.0 option go to
http://www.geocities.com/shvoldum/main.html
for more info