The 700 is actually used with far more horsepower in the racing mower world, and is known to be very reliable. However torque loads are what kill them, the cases are not very thick, and the output shaft is usually supported by bronze bushings - I would not design a utility vehicle around one.
If you REALLY had your heart set on it, i would design your frame to incorporate extra support bearings for the input and output shafts. Limit top speed to 15-20.