Since you eliminated the C-54 Skymaster by Douglas, I don't have a clue. Boeing made some cargo units, but they weren't like the photo at all (as I recall), and it seems that the Lockheed versions were all twin verticle stabilizers like the Constellations. The Skymaster was the one I first thought of when I saw the pic.

Apparently not the answer. I dunno.

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Happy Trails,
Clint.