In the B-25, the original "dorsal turret" was a single machine gun that was raised up and out from the empennage through an opening that was created once a window was retracted.

It appears that the large patch on the empennage covers the original location of the "aft gun"
Is it possible that this large patch is a skin that was applied to the original configuration as this section of the plane had not yet incorporated the structural change from the original drawings? The photo below shows the size of the "window".

Additionally, I am not familiar with any version of the B-25 that had a life raft compartment aft of the forward of the center section.
Further, is it possible, that in the first photo posted by Shay, what we are seeing in this photo is aircraft that are destined to move down the ramp to a location at Inglewood, where the turret assemblies will be added to the airframe for fly away? I am however, uncertain of this, as I have a factory photo of B models in production minus outer wing panels that show the aft turret installed in the assembly area.

Hmmmm….. the Nose on the Russian B-25 isn't like any nose on a B-25 that I have never ever never seen
All of this is just my opinion of course, thoughts, ideas??
All of the above photos are from my collection acquired from Earl Blount NAA/Rockwell