How do you not see a B-17 in a planned demonstration flight? If this was anything like other demonstration flights I’ve seen, all of the planes flying at the time were part of a rehearsed sequence. I’ve never seen such a flight where another aircraft would make a maneuver like the P-63 did to buzz another aircraft, so someone must have been out of position by a significant amount. And if it wasn’t a rehearsed sequence, there must have been a serious break-down of air safety at this event.
In any case, this is much more than just two vintage aircraft colliding, and will come down to more than just “Failure of the P-63 pilot to maintain visual separation with the B-17”.