Andrew sez "... I'm guessing it is some sort of fuel pit."
I agree - What looks to me like a fuel hose is visible in the shadows curving up to the port side wing leading edge, and a person standing on that wing paying attention to what I'd guess is the fuel nozzle.
Agree John. Weren't white coveralls standard dress for mechanics and such in that era? The person who seems to be seated at some kind of control panel on the right side may be monitoring the pump controls. Looking close, I think he may be military. A Navy Chief Petty Officer in khakis? Sure looks like the top of a chief's hat to me.
Ric, were there any notes, dates or other kind of documentation in the folder? Other (better?) photographs?
I'm wondering if this isn't the final fueling before departure the next morning, right after the a/c came out of the hanger with a bright, shiny new patch.