Torque is the factor not horsepower. Most trannies will handle more than what they are rated for.
http://www.gminsidenews.com/index.php?page=trans_guide
http://en.wikipedia.org/wiki/Tremec_...0_transmission
The rear end should handle more than what the GTO was capable of, it is an improvement over the GTO V-body platform. Hard to tell, autos are more forgiving than manuals on the drivetrain.