Preheat oven to 300 degrees and spread the cubed cornbread and sandwich bread onto a baking sheet.
Toast the bread cubes 20 - 30 minutes, or until lightly browned and starting to dry out. Set aside and turn the oven up to 350 degrees.
Melt the butter in a large skillet over medium heat. Saute onion and celery until soft. Set aside.
Crumble the bread into a very large bowl. Add the onion/celery mixture, salt, pepper, parsley, sage, thyme, and garlic powder.
Fold in the eggs, then add the chicken stock a little at a time. The dressing should be moist enough to clump together but not so wet there's liquid in the bottom of the bowl.