There is a difference between cars with a first date of registration before and after Jan. 01 1973. That's why all your pre-1973 cars have "oldtimer plates" (starting with two letters, followed by two groups of 2 numbers) and your 1973 Riviera has a license plate with 2 numbers, followed by two letters, followed by two numbers. My 1973 Riviera has a first date of registration of June 30 1972 (which is wrong because the car was build in the second week of November 1972), and because of that I could get an "oldtimer plate": DE-68-25 BTW: Welcome, Coen !!
Did you check my photo-thread about American station wagons in Europe ? You will be surprised how many wagons left North America for a new life in Europe: (Some wagons were even built in countries like Poland, Sweden, Belgium, Switzerland, etc.) Click here