Cut an X on the bottoms of peaches, carefully cutting just through the skin. Fill a large Dutch oven with water, and bring to a boil. Immerse the peaches for 20 seconds, remove with a slotted spoon, and plunge into ice water. Slip skins off peaches using a paring knife (skin will be very loose). Cut peaches in half; remove pits. Slice peaches to yield 12 cups.
Preheat oven to 350°.
Combine peaches, 3/4 cup granulated sugar, and flour in a 13 x 9-inch baking dish coated with cooking spray, and let stand 30 minutes, stirring occasionally.
Combine 1/4 cup granulated sugar, orange rind, orange juice, butter, cinnamon, and egg whites in a shallow bowl, stirring with a whisk. Trim crusts from bread; cut each slice into 2 triangles. Dip bread triangles in the orange juice mixture; arrange on top of peach mixture. Sprinkle turbinado sugar over bread. Bake at 350° for 45 minutes or until golden.