I haven't moldboard plowed a big enough patch to plow in both directions, generally with a mp I would just do gardens and leave one furrow on one side of the garden. When someone would plow a larger patch and would want a furrow on each of the outsides of the field what would you do in the center? Leave a strip of unplowed but covered dirt in the middle? So if you were using a 14" bottom plow you would have 28" of covered dirt unplowed, 14" of turned dirt from the first pass in each direction. Or would you try to plow the dirt the was turned over from the first pass and the virgin dirt underneath?