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Packard Merlin splined for Hamilton Standard props. The standard spinner did not fit over the HS hub.
You've now touched on the next bit of investigation that I'm doing as I'm investigating whether or not such examples made it to the RAF and what they might have done to the spinners. It seems modern flying examples, many if not most of which are Mk XIIs, had custom spinners made that are more elongated than typical Mk II spinners. Like this one:
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..and this one. Compare with the one in the background.
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