but I wonder even if the B-17 had been visible, would he have seen it
Tracing out the tracks of the two aircaft from when the P-63 rolled from an easterly heading to northerly the relative bearing between the two remain pretty much constant, in the order of 40-45°, such a position would have the B-17 placed close to, or hiding behind the P-63 forward door structure according to plans, from rolling on to the northerly heading to collision was of the order of 20 seconds, relative altitudes not given, only P-63 reported, the maximum lateral separation they had was of the order of 2,700 feet during northerly flight. No, or very little relative motion, camouflaged B-17, NTSB report will figure it all out.