Whats the point in adding weight to your car by putting in a larger case diff than you need? My car has almost 300,000 on it with the original 4.10 small case lsd, and a little motor work. the diff is still working. a small case 4.10 can obviously handle more power then the m42 can make in its original form. For this reason, I do not see any need to put a larger case diff in a an m42 unless your doing some serious work to it.