I seem to remember that it was one of the ball turrets that were cut in half and attached to the five B-17's for the film Tora! Tora! Tora!
It was easier to bolt them on for the film than cut a hole and have to go through that process.
As a side note, if anyone has watched Jeff Ethell's Roaring Glory Warbird series on the B-17, they used Fuddy Duddy for the subject aircraft, but if you notice, the aircraft inside has a complete ball turret and a complete top turret. Fuddy Duddy didn't have those. When were were filming the series, I made note that it didn't have them for the "re-enactment" scenes, but that right next door on the Geneseo ramp was Nine-O-Nine, which did have them. Top turret, radio room and waist scenes were all shot inside Nine-O-Nine, while the cockpit and bombardier scenes were shot in Fuddy Duddy.