Well, it looks like some weight was out of the GTO
"The car was ran at the track with simililar form compared to LS1Mellisa, All seats, skid plate, gas brace, tow brace were all removed."
Also, the car was cutting 1.5x 60's which is way better than most of the GTO's running around with that power level. To run 11.8x's @112 you are either hooking really hard, or the car isn't full weight. It looks like both are the case here. Either way, that GTO is getting it done for the little bit that is on it. Just found another little bit of info. GTO owner estimated a 3400-3500 lb race weight for the car. My friends 04 was 39xx. There is your answer. A lot of weight reduction.
The mustang posted is the first one that has a full exhaust, tune, and tires. I have a feeling that it will run better with time.