The puzzle in the second volume of The Art of Computer Programming has been solved! The composite cofactor of the public key was the product of 91-digit and 97-digit prime numbers:

91-digit prime factor:
4812118250596034474977589134243684231351843343856605196610181688401638676082217744120094291

97-digit prime factor:
1414213562373095048801688724209698078569671875376948073176679737990732478462107038850387534327641

With these and the previously known 25-digit prime factor, 1144729885849400174143427, we are able to decrypt the RSA-encrypted literary quote. The quote is the following:

His remarks (as reported) were as follows:--
"O Rowty-owty tiddly-owty
Tiddly-owty tiddly-owty
Highty-ighty tiddly-ighty
Tiddly-ighty ow."

--G. K. Chesterton (1905)

This is from The Tremendous Adventures of Major Brown, the first in the collection of short stories The Club of Queer Trades.