Before the US officially entered WWII, a small force of volunteer pilots fought for the Chinese against the advancing Japanese invaders. This elite group became known as the Flying Tigers. Eventually, as the US entered the war, the Flying Tigers were mostly absorbed into the 14th Air Force.
Bromley states that he will destroy all four guns around the temple along with several friends as he states in his dialog, but in the cutscene he rides with Sikorsky helicopter, which he is the only one that seen in the helicopter.
It is highly likely that the Chindit's deaths are canon, as they are not seen evacuating the temple, regardless if they survived or not.
According to the storyboard, Tanaka was meant to steal clothes from a Japanese soldier, wheel the player into the temple's banquet, draw the guards from the prison area into the cafeteria with the promise of "free sake" and sneak the player into the prison area under the guise of a new prisoner.
In reality, Yamashita's Treasure is a legend that has yet to be found. Alleged locations or explanations include the treasure was sunk in the South China Sea when U.S. airforces sunk Japanese merchant ships, was found by then-Philippine President Ferdinand E. Marcos during the 1960s-1970s, or it remains undiscovered to this day.