As per prior posts, you'll need to set up the box blade angle correctly, and make a zillion passes over the patch of soil you intend to cultivate, but it'll eventually work. That said, there's no way you're going to get the depth of soil disruption that a large tiller will accomplish. Me, I've no tiller, and am resigned to renting a walk behind unit each year prior to planting my modest garden plot. I've not done that yet, as I still need to fence the area, or whatever planted will become deer feed. Anyhow, in the area I intend to garden, I first used a subsoiler to get things broken up 12" plus deep, then ran over the area with the box blade scarifiers. Thereafter I dumped 2 loads of topsoil on the cut up surface, and ran a middle buster (on same shant as subsoiler) through it to mix up everything.
So, in a couple of years when I actually start a garden, and rent the largest walk behind tiller I can find, things should be pretty well ready to go.