Can you fit muck forks (prongs as opposed to a flat bucket) to the front of the tractor? The stuff should lift up in large pancakes with enough oomph. You might need to go hand gripes for the very bottom layer, or may find you can get almost all of it with the tips of the prongs, without damagjng the cobbles. (This is my thoughts, not something I have personally done. We always have had either cement or earth floors.)