Speculation as a profitable profession is a 37 page book, with a second volume of charts (no volume 3 that I ever found) and it has nothing on the 7-10 rules.
I have the entire WD Gann masters course, and PDFs of everything WD Gann ever wrote. The 7-10 rules are about 2 paragraphs long, and are referring to a Cotton trade, which is used as the example. Yes, it's mentioned elsewhere, but there is not 3 pages on it.