Howdy, I had to go a long ways back to get to this topic, so we better say something. Recently, Joe and I were visiting about the Wallis 15-25 dilemma. AKA the Model OK, Some or most have the steering shaft that goes to the steering box on the front of the Tractor, where as some have the steering that is similar to an early 20-30. It took me a few moments to remember, but I remember back in the Days of the Wild Harvest Show and Banquet, we were at Madison, South Dakota. And during the daily Parade I had the great fortune to sit on the groud, under a shade tree with Gene Schmidt. In that hour and a half or so I learned more about the Wallis line than I thought there could be. Gene explained to me how, as improvements were made they cold be utilized on earlier Models keeping them useable, unlike competitive companies. Another topic discussed was the OK/OKO differences. Gene explained as the Wallis Line continued to evolve to the OK more modifacation were being made, one in particular was the Steering. By changing to the newer style Steering,. which was introduced and continued on into the 20-30, this marked the end of the OK, and the15-25 was now called the OKO. I do not now remember if there was a cutoff, and became this, or if Wallis made a few to test and follow in the field before changing completly. Gene was truly a Wallis Authority and after all these years, the questions I have he could answer is greater than then. Hopefully this helps answer some questions.
On another note, another topic Joe and I were discussing was the year the Wallis Cub Jr was introduced. Joe and Tom had scoured all information and found nothing to date the introduction before 1917. Advertisements in Trade magazines confirm this. I did however find a dating of sorts to this. When Massey Harris purchased the J I Case Plow Works, with the Wallis line they made a Sales Booklet, including Testimonials, from owners of Wallis Tractors. In this Brochure under Testimonials from Iowa, is one from my Great-Grandfatather E.H. Pace and his 1916 Wallis Cub Jr. Serial 10056. Sure makes you want to scratch your head. As always we keep looking. Well Happy Trails, Tim Pace