Hadn't thought of that! And considering that based on what I calculated in the post he goes off the edge at about 70mph, he probably needs way less that 258 feet right?
The 70mph is horizontal velocity, gravity is vertical acceleration from 0. Total velocity is sqrt(sum of squares). It's unclear how much horizontal velocity the train would lose due to air resistance and due to the unclean launch from the ravine. (Would it fly off the end of the track, or tip off the end and tumble down?)