That firebox is a little on the big side, but it should be fine. There could be some draft issues, but I don't think it will be enough to cause problems. I believe, as long as you can control the heat inside it, it will work. More problems come from boxes being too small than too big. Too small means the fire may not be big enough to properly heat the CC. Too big just means more fuel for the fire. This could be a huge advantage if you use the minion method on long cooks. For shorter ones, just use less. Good job, brother.