At the end of the day, without any documentation to substantiate the "Imported by Mercedes-Benz to North America for the purpose of Rally driving" claim, then there is no basis for it. And I'm guessing if the documentation was there, then this question wouldn't be being asked.
And I guess the question would be asked, if it was indeed imported for that purpose, then how come it never rallied?
Sorry bhmc. Looks like whoever sold or traded this car is spinning a yarn.
You might also want to be careful that your listing for it doesn't constitute deceptive advertising, as well.