I've never tried making this gluten-free. A one-to-one GF flour will probably work well.
#1 2 cups granulated sugar 1 tsp salt 4 large eggs 1/2 cup oil 2 tsp vanilla #2 2 cups flour 1 tsp baking soda 1 Tbsp cinnamon #3 4 to 5 apples, coarsely chopped Beat #1 until fluffy and well mixed. Add #2 and blend for 2 minutes. Sprinkle some loose flour onto apples to coat, then add. Mix well. Pour into greased 9x13 pan. Bake at 175C for 45-55 minutes. The last time I made this I reduced the sugar to 1 1/3 cup and used 1/3 cup oil. It was still yummy.