The factory data supplied by Ford themselves to the Motor Vehicle Manufacturers Association and published along with every other specification for the car you can think of.
Their definition of curb weight is full of fluids, ready to drive, but without cargo or passengers. The consensus seems to be although most GT's came with A/C because the people paying for the GT package tended to want more heavily optioned cars, they could be ordered without it. Maybe it was standard but could be deleted. Otherwise the only thing the GT package really got you over a 5.0 hatchback was the body cladding, the seats, the foglights, and the 2-tone paint availability, and maybe "convenience group" interior lighting.
LX coupe 5-speed 3010
LX Hatch 5-speed 3069
GT Hatch 5-speed 3144
LX Convertible 5-speed 3231
GT convertible 5-speed 3365
LX coupe AOD 3076
LX Hatch AOD 3135
GT Hatch AOD 3210
LX convertible AOD 3297
GT convertible AOD 3431
These are the base weights for each model. Add to them the following options weights accordingly:
Power Locks 6
Power Window 6
AM/FM Cassette 2
Premium Sound 5
Radio Delete -9
That's EPA mileage. Derived from a government-mandated test cycle; not Ford.
"Curb Weight" is specified according to SAE standard J1100 "total weight of vehicle including batteries, lubricants, and other expendable supplies but
excluding the driver, passengers, and other payloads"
Mustang Monthly Jan 2015- Feature
5.0 Mustang & Super Fords July 2005