NS has taken nearly 275 C40-9s and C44-9Ws and converted them to "AC44C6M" models using their own shops and outside contractors. More conversions may be planned. The 4121 was worked at the Roanoke, VA shops. Some of the first units in the series are specially painted and look pretty cool. The 4000 was the first. [January 2019, Asheville NC]