Drew, check this out:
B-25
This is an excerpt from that webpage:
For the film, mock upper turrets were installed. To represent different models several aircraft had the turrets installed behind the wings representing early (B-25C/D type) aircraft. Initially, the camera ships also had the mock turrets installed, but problems with buffeting required their removal.
Granted this is Wikipedia, take it for what it's worth.
Hope it helps.