monocoque noun (mono·?coque | ?mä-n?-?k?k): a type of construction (as of a fuselage) in which the outer skin carries all or a major part of the stresses (courtesy Merriam-Webster).
You can really see how the body is a part of the "frame" unlike other conventional locomotives thanks to this one being stripped of the prime mover, alternator and other bits and pieces that make it go. The artists at Beech Grove perform heavy overhaul procedures on the GE fleet, which have seen billions of miles.