What year gto ? 04's are 5.7 05-06 is the 6.0 LS2, the 05-06, maybe a little closer to what you said, but still not gonna get there without a cam.

Heres another one to compare, 6.0 car, 224/228 cam, ported stuff, full exhaust, 422 rwhp / 414 rwtq.

2005 Pontiac GTO LS2 JBA Headers Dyno Sheet Details - DragTimes.com