I don't think those AMG alloys were ever a factory option for the R129 here (that was always a multi-piece design), but they'd have been available to order as an 'accessory' (like the AMG back box). Or somebody fitted a set later in the car's life. I agree they are good-looking wheels!
Sport models here in the US got 18" monoblock wheels. There were two styles available with the later style design to accommodate the big brakes in the 99+ cars