Well I was a bit wrong, too….it seems to be a DC-7B which suggests it wasn’t one of the original American Airlines fleet (they sponsored the basic DC-7 against Douglas Co. wishes). You weren’t alone, AJ Jackson fell for the D7C graphic trick which Dan Air used ,too and the RAF Museum have got their Charles E Brown BOAC DC-7C pic listed as a DC-7B 🙂
Edit …I think there were two types of DC-7B…. S.A.A (and maybe Pan Am) had DC-7Bs with saddle tanks at the back of the engine nacelles (DC-7C style?) which the US Domestic ones in your pics lack,
see
http://www.abpic.co.uk/photo/1142121/