I have tricked several wheat eaters with this recipe. Very tasty and not gritty like typical gluten free recipes. Our normal grocery store carries soy flour and shouldn't be too hard to find. Definitely worth using! Adds protein and fiber and I think it helps with texture. You could probably get away with omitting the teaspoon of guar gum, but I have it on hand and use it.
I've used both milk, lactaid and soy milk for this recipe without any problems. I have also used pure pumpkin and pumpkin pie mix (this will make the batter more watery, so bake a little longer). You don't have to use the chocolate chips, they'll still be quite tasty!