I would ask you a question, what would take the most time and money to accomplish - moving the pilots positions aft while shortening the turtle back, or just removing the nose at the bulkhead just forward of the windshield? From the pics, it appears that they removed the nose and replaced it with the engine and its panels. Plus the weight and balance would be easier to work out. Plus, an original nose could be found and reinstalled when testing was completed and the a/c sold.
When testing was completed, the a/c was sold, a new (to the a/c)nose was installed and the a/c was restored as a B-17G, named "The Liberty Belle" and operated on the Warbird Circuit until she crashed and burned in 2011.