Visual Contact
around 8 seconds to 3 seconds before impact the B-17 would have been visible at around 30-40degrees right of the nose of the P-63, which is about the time the pilot is setting up his turn to the left. At 3 seconds or so before impact the P-63 rolls into a left bank and the B-17 is obscured from that point until just before impact. The left wing tip of the B-17 would have come into view immediately before impact, far too late to avoid the collision. The video doesn't readily show what the P-63 would be seeing before the 8 second point before impact, there will be video out there, it just hasn't surfaced as yet.
The low differential in speed increases the angular scan region required to clear for traffic, a lookout to around 70 degrees off the nose would be required to visually clear this traffic just on the relative speeds. The traffic that the P-63 was following was off in the opposite direction to the proximate traffic, left of the nose, around 10-11, vs the B-17 at 1-1:30 or so relative clock position.