This looks very close to what Orgrans uses from reading the list and their mix is the best. Littlelost, cornstarch is gluten free, it's wheat, rye and barley that have gluten. I've been using it for a long with no problems and I can't even tolerate cross contamination from touching something.
I haven't tried this recipe yet, but everyone looking for a gluten free mix should be aware that corn starch, and for that matter any corn products, are not gluten-free. They are far lower in gluten than wheat or barley, but people with celiac should still avoid it.