Hmm. A diligent search of all nouns of the correct length in BRB (thank goodness for the app) with the restricted crossings lead to very few which fit, of which all but one are clearly not right. But that one isn't all that good either, which (given the precision of the rest of the quote) seems unlikely. Without giving too much away the number of letters I have changed is the square root of the first digit of the square root of the puzzle number.