I don't think anything has be written on trains at all, stat wise.
They are big, heavy vehicles that make tanks look small. For the most part, anything short of a large explosion is not going to do much structurally to a train.
So this may just be a place and time for some "GM handwavium". Set the stats at what you think is right, and adjust from there.
For what its worth, during WW2 trains that were attacked directly were done with 500lbs bombs or clusters of rockets, usually fired/dropped from planes. However, this was rarely effective against the train itself. The tracks the train rides on was a different story.
Allied fighters would bomb the tracks and destroy them, thus making the train useless in transporting material until the tracks were fixed.