Further photographic considerations.
1. That is a very nice air-to-air photograph, and such things aren't achieved easily. If the feathering was shenanigans, it was highly premeditated and involved the co-operation of at least one other crew. More likely, it was in some way official.
2. The engines pretty certainly really are stopped. Given the very high level of detail in the photograph, it was pretty certainly made with a large format camera (prob 5x4 inches). The shortest shutter speed that would possibly have been available on a lens for that size would have been a nominal 1/500 sec; for a variety of reasons, the shutter would have been actually open for about 1/300 sec. It seems Merlins came with reduction gearing ratios between ~0.4-~0.45 (
Gearing), so we might imagine the propellors would have been rotating at 600 rpm or more in normal flight. That's 10 revs a second, and in 1/300 sec 12 degrees, which would produce noticeable blur.
Nothing about the aeroplane, I'm afraid, but I hope it helps define the circumstances.