I talked to the guy that is doing this and looked at his design.  I thought it was well designed and a logical approach.  The water pump is gear driven and everything is high quality.  I feel that the only real advantage is that liquid cooling can allow the compression to be raised somewhat because of the cooler cylinder head surface temperature.  And the volumetric efficiency might go up a little because of less inlet air heating.  The liquid-cooled cylinders themselves are actually lighter than the air-cooled versions, but adding the other stuff, including the coolant, raised the installed weight, but not by much.  In theory the required radiator can cause less drag than the cylinder fins, but you need more air to do the cooling.  the cylinder fins of an air-cooled engine are at maybe 350 degrees, while the coolant is limited to around 200-240 to keep a margin below boiling.  The bottom line is you need more air, but the restriction to the air flow is less - nominally a break-even proposition.  The higher the speed the more the equation goes in favor of liquid cooling.  And if you want to add more boost (more power) the cooling is mostly limited by the radiator size, not the cooling of the cylinder itself as is the case with air-cooled cylinders.  A liquid cooled TSIO-540 for Reno?  TSIO-720?