Well the 50 year-old T-2C has a better power to weight ratio than the T-45. 2.25 lbs of weight per pound of thrust at max weight for the T-2 compared to 2.54 pounds for the T-45. It would be a lot easier to retrofit an even more modern turbofan to the T-2 design than it would be to make a twin-engine goshawk. If there are any magic aero features of the goshawk they are not readily apparent.