I wonder why a regular He-111 wasn't used. The twin fins and second dorsal gun position are puzzling to me. If they wanted a scarier looking real airplane with twin fins and two dorsal gun stations, there's the Ju-290. Artistic license at the behest of the director? Copyright? Board of directors meddling?
In the original film, the flying wing had what looked like a Boulton Paul tail turret when a Ikaria cone turret would have been more appropriate. Sorry, I'm just a Luftwaffe modeler thinking out loud.