That first shot does look a bit risky, but I'd bet you that was just some Hollywood magic. I would imagine that the flyable (gas filled) B-17s were actually much farther in the background then they appear. By stacking the aircraft like that, the field of depth (through the lens) shrinks and can appear to be smaller than it actually is.
I'm currently creating a 1/72nd diorama of the Haleiwa Scramble, involving a P-40, the 1940 Mercury (below), the ground crew, pilots, and film crew. It's taking longer than I'd like to admit but it's interesting to research more on the scene. The red 1940 Mercury Convertible was supplemented for the actual (original) 1940 Buick Convertible that Lt. Taylor owned and had painted orange not long before Dec 7th.
The location for the airstrip was different too for filming since the actual Haleiwa was overgrown and unavailable in 1969. I think they used one of the runways at Bellows for this scene. Anyone know for a fact?