but by googling
guiness "longest sentence"
I got several interesting hits, including this one:

Linguist Steven Pinker illustrates this point in his book “The Language Instinct” by improving on the Guinness Book of Records entry for the longest sentence in English: (1,300 words, from William Faulkner’s “Absalom, Absalom!”): They both bore it as though in deliberate flagellant exaltation...

Steve Pinker’s new submission: Faulkner wrote, “They both bore it as though in deliberate flagellant exaltation…

edit: searching for "guinness" works well too.