Kawasaki uses the SAE1940 standard which states:
Peak Horsepower (HP) specifications for general purpose engines are calculated pursuant to the Society of Automotive Engineers (SAE) J1940 for horsepower ratings - calculated with the air cleaner and muffler removed, per the SAE standard. Actual engine horsepower is lower and affected by, but not limited to, accessories (air cleaner, exhaust, charging, cooling, fuel pump, etc.), application, engine speed and ambient operating conditions (temperature, humidity and altitude). The reason for this standard is to provide consistent measurement to customers who may want to control the intake and exhaust features of the engine. (ml-small-engine-services).
So a 27hp FX751V engine net hp could be 25 or 24hp if not less. However, the bore on the FX751V is bigger than the FX730V 26hp, so you will get more torque out of the FX751V. Kawasaki's website only shows gross hp and torque. I would think the torque will be around 47 to 49 ft lbs if not less depending upon what the tractor company adds to the engine.