The thing with a conversion is that you need to keep about the same power as with the original engines so that the aircraft will behave similarly in an engine-out situation. If you went onto one much more powerful engine then the amount of control from the rudder would be quite insufficient. The Twin Otter, for example, limits the amount of power on the later versions of the PT-6 to that available on the original engine, for this reason.
One "gotcha" with this DC-3 conversion is that functioning autofeather is a required item, or so I have been told. Without it an engine failure immediately after lift-off can be a serious problem.