This picture shows the completed gantry and a good bit of the boom in place. At this point the machinery deck is fully enclosed and the electrical work is probably going on inside.

Note the two I beams sticking out of the rear of the machine. These are the side rails for the overhead crane inside of the GEM.

 Most of the rear of the machine opens up to form a large doorway. If a motor fails and needs to be replaced, it can be lifted off of it's mountings, carried to the rear of the machine and set on the ground behind the GEM. A new motor can then be lifted into the machine and set inside to replace the old one.

These overhead cranes have both front to rear and side to side movement capabilities , and can cover nearly every square inch of the machinery deck.