Depends on exactly what GT-40 motors you're talking about as there are several varriants of the motor.
The most well known is the SVT GT-40 motor used in 93-95 Mustang Cobras. They used a GT-40 upper/lower intake, iron GT-40 heads, 1.7 Crane roller rockers with a slightly modified cam over stock GTs. The motor was rated at 240 bhp.
The 96/07 Explorer used a planner/slightly more restrictive upper/lower GT-40 intake setup, and GT-40 iron heads rated at 210 bhp. As stated, after that they used the better flowing GT-40P heads rated at 215 bhp.
The least known motor was the SVO GT-40 option made available in 94/95 for approx $2500 over the MSRP of a regular GT. The SVO GT-40 used a tubular GT-40 upper/lower (pretty much same as a Cobra but without the Cobra plaque), GT-40 X303 aluminum heads, not sure on the cam used though, and 1.7 roller rockers. The motor was rated at 290 bhp, and for an additional $2000 SVO and Ford would add in a Powerdyne supercharger rated at 6 psi, a 9psi option was also available for a few more dollars.