Either here in the US or overseas where they are manufactured? I only know them as racing cars.

The CLK MBz could be street legal if it were a U.S. model and passed all the emissions control tests in the state where sold. The GTR qualifies as a custom built race car and would have to qualify for importation into the U.S. as a personal vehicle intended for re-export within one year. California would likely pose a referral to an Air Resources Board, referee station, where a certification might be obtained to legally register the GTR as a custom historical vehicle.