I am always looking thru Jack's books . In the latest book there was a caption under a square G B 67 , " outside markers , not sure if authentic " . Here is a G B 67 that I have , and it had outside markers . It doesn't show up real well , but the 10 gallon marker was riveted on the outer edge of the lower cylinder base . I too , I'm not sure if authentic , but they were on the outside when I got it off a farm 20 years ago ?