- 6 Inch Kenworth W900L 40" Box Step OEM Style Elbow Exhaust KitStarting At$2,417.40DF-KH-605052CP-BULL6 Inch Kenworth W900A Under Frame OEM Style Elbow Exhaust KitStarting At$2,379.29DF-KB-605048CP-BULL6 Inch Kenworth W900B Over Frame OEM Style Elbow Exhaust KitStarting At$2,349.42DF-KC-605048CP-BULL