One engine that looks really promising is the 3.5 in 2005 they had the slk 350 at 268 hp and in late 2007 upped that to 300hp this for an NA would be night and day difference. A mild supercharger or Turbo on either of those engines would yield much greater numbers then the SRT-6 especially on the post 2007 motor. Right now I'm sure there very pricey but in a year or two when the Crossfire motors begin to get up in mileage this might be an option.