Hello. First off welcome to the site! I hope you find it as useful and enjoyable as I have.
The GT option did not mandate a 4 speed tranny. Many GT's have the 3 speed unless the customer also opted for the 4 speed. The car you're looking at should have front disc brakes, fog lights, dual exhaust w/ the trumpets exiting through the rear valance, styled steel wheels, GT stripes and badging, and 5 dial instrument cluster. Make sure the VIN on the door data tag and the VIN on the inner fender apron both match.