I was in need of another shavehorse recently for a class, so I grabbed a dumbhead swing arm that I had laying around and cobbled together a horse. This part was an experiment that I had tried when looking into making an adjustable shavehorse. I rejected it because it had some short grain issues that I thought wouldn't stand up. But after using it in the class, I realized that the shortgrain issues that came with sawing the parts from a board could be sidestepped by using hickory dowels for the "teeth". It took me all of 15 minutes to retrofit with dowels and I have been using it with great results. The video is clearly a quick shot, but I think it gets the idea across.
The one drawback to this design that the "smarthead" solves is that the foot treadle rises when you adjust it, but so far, that hasn't been annoying enough to overcome the simplicity and the strength of the concept. Ideas aren't always linear, this one sat for a couple of years, but I thought it worth sharing for those looking for simple solutions. The dowels are set at a 23 degree angle (probably variable) and are 5/8".