Quite possible that a lumbering B-17 couldn't have made a significant difference in separation but I see no reaction at all in any of the video.
My guess is that even if someone on board saw the incoming P63, there would've been insufficient time to:
- realise it was on a collision course
- call that to the pilots in a meaningful way
- for the pilots to take effective avoidance action.
Looks like there would've been only a few seconds for the realisation of the danger to be processed, if anyone indeed saw it.