I don't know why they would post a pic of the "bottom". I do wish there was more on this. It would make a neat model. I could extrapolate something in 3D but I hate guessing on stuff like that because the rivet counters always jump in, of course, rarely do they have any better pictures. If someone found some really good line drawings, or pictures I could work with, I could make a model that could be greebled to life.
It would be great if you did find some more reference material. This is one of my favorite all time movies. The "Doc's" small flying saucer, though not completed, was pretty neat too!