That guitar is definitely NOT a Gibson. That headstock design is characteristic of the D'Angelico. In fact, this guitar that Jim is playing must be Chet's guitar. Jim may have borrowed Chet's guitar for the session or just for a few minutes.
Check out the zoomed photo of the headstock design:
Now, here is a photo of Chet's 1950 D'Angelico Excel.
EVEN IF the guitar that Jim is playing is not Chet's guitar, it's DEFINITELY a D'Angelico. In addition to the headstock shape, compare the headstock inlay design as well as the length and shape of the name (logo) at the top of the headstock.
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