As in a previous thread, I can confirm from Brewster's Dictionary of Phrase & Fable that a "castor" was a hat covered with beaver skin (think of a Dickensian stlye top hat - skin is more waterproof than felt, the other usual material)

Also, "nine tailors make a man" may derive from the fact that, on the death of a man, the church bell rang nine "tells", (three sets of three), whereas if a woman died it was six tells (three twos). Thus "nine TELLERS make a man", later corrupted to "nine tailors".
Maybe.

Andrew