But it still isn't going to be plug and play.
You would need the GT gas tank unless the 3rd gen is a 97 and probably the pump. The 3rd gen used an electronic speedo and the GT does not so that would have to be hacked together. The dash wiring is completely different, nothing will plug in, everything will need to be soldered and heat shrinked together. Basically rewire the whole car. It might be easier to just swap the GT dash, heater/AC, ect into the 3rd gen if it will fit.