Why not go the v-8 route, it will be a blast and it probably will cost as much as the Supercharger kit from Germany or Renntech, and you will be able to make more power with a turbo at a later time.
I think with a ecu tune on the MBZ 5.0 they can put out well over 350 hp and who knows how much insane torque it will produce.

Either way you need to get a good stand alone ecu probably cost $2,500. then the motor most likely from a wrecked mbz, used is $4,500. get it tuned and running and I'm sure you'll be a grinning fool. If you still got some cash to burn, bolt up those turbos and start breaking parts!

Otherwise the smartest route is to buy an srt6 and forget about all this dreaming.