I think it's be listed incorrectly as the CLK430, as the W209 didn't come as a 4.3, only 5.0:
www.spark-plugs.co.uk said:
Results and information
Manufacturer MERCEDES
Model CLK430
Engine Size 4.3 L
No. of Valves/Cylinders 24V / 8Cyl
Variant None Specified
Year of Manufacture 06/02 ->
Power output 306 BHP
Standard gap setting 1.0mm
Part Number Short Code (aka) Price (£) Per Plug Qty
KC11PYP OE149 9.21+vat