I have several books on original powder horns and that's where I get most of my patterns, I can copy anything I see on a horn, names, banners , eagles, rivers, maps, stuff like that but the photo image is beyond me at this point. I have Blackie Collins book but didn't get much out of it. I've made that tool just as you suggest and it works well and just a scribe or a needle stuck in a dowel works for some applications.
Deadeye