What would the process be if someone were to... just for speculation, put a Mercedes OM-617 Turbo Diesel into a First Gen pickup. Would it be black labeled or would it just have to pass numbers for that engine? I happened to have a low mileage (283,000) OM-617 sitting in my garage w/ a blown turbo. I wouldn't recommend doing that swap w/ a Mercedes diesel because they are VERY low quality and have reliability issues, especially with the low quality cranks and bearings used on the turbo bottom end. They make low torque as well.
