Place this file in the folling places

Western Pacific DCSV
C:\Program Files (x86)\Steam\steamapps\common\RailWorks\Assets\DTG\GP40-2Pack01\RailVehicles\Diesel\GP40-2\WP\Engine

Union Pacific DCSV
C:\Program Files (x86)\Steam\steamapps\common\RailWorks\Assets\DTG\GP40-2Pack01\RailVehicles\Diesel\GP40-2\UP\Engine

Norfolk Southern DCSV
C:\Program Files (x86)\Steam\steamapps\common\RailWorks\Assets\DTG\GP40-2Pack01\RailVehicles\Diesel\GP40-2\NS\Engine

Denver & Rio Grande Western DCSV
C:\Program Files (x86)\Steam\steamapps\common\RailWorks\Assets\DTG\GP40-2Pack01\RailVehicles\Diesel\GP40-2\D&RGW\Engine

CSX DCSV
C:\Program Files (x86)\Steam\steamapps\common\RailWorks\Assets\DTG\GP40-2Pack01\RailVehicles\Diesel\GP40-2\CSX\Engine