You can grab an Athearn RTR P42 in the Northeast Direct Amtrak paint scheme for around $40 at TrainWorld and other places... It might be more economical to buy that and swap in your P40 shell if the paint scheme and details are different.
Hope this helps!
TomDiehl wrote:The power trucks from Athearn are part numbers 36540 for the front and 36550 for the rear. Then you'll need the spline shafts and couplings, plus the mounts for the motor. Adding all this up, you'd probably do better to just buy a powered unit.