With the size and HP of tractor that you have, I dont think it practical to try to dig that much with it. You just dont have the weight and HP needed to move dirt or drag it with the box blade. For that much dirt, I would contract someone with a dozer to come in and cut it down, slope the cut and get it done quickly before the winter freeze sets in. When the ground freezes, you will be out of luck till next spring as even the largest equipment wont dig in frozen soil.