This is a little complex, but let's simplify it: 1 - Note the double negative in the sentence: "may not have been" and "not so prone". 2 - Put aside the reduced relative clause "surprisingly untrammeled by the prudishness of his time", to make the meaning easier. 3 - "had he lived" means "if he had lived" Now we can re-write it as: "Perkin's wit , may not have been as racy if he had he lived in an era not so prone to blushing".
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