I'm certainly not trying to disparage John Rivers, as you think highly of him and his brisket. But, unless John smokes briskets in a Smokin-It, and only does 6 lb flats (I suspect not), I wouldn't put much stock into the "18 hour" comment. If you smoke a 6 lb flat for 18 hours, you will probably be able to re-sole your shoes with it. Rely on internal temp, not time!
Also, smoking at 175 is fraught with danger. The meat will sit at an unsafe temp far more than it should, and you're likely to run the risk of food-borne bacteria. 175 is not a safe temp to smoke at, in my opinion.
My 2ยข? Follow some of the proven methods on this site, and smoke by internal temp at a reasonable smoking temp (225). Don't need anyone getting sick because John Rivers said to smoke at 175!