It’s definitely not made from spare GTO parts, two different cars
GTO was only meant for a 3 year run from the very beginning of only 36,000 units.
I’d say they did pretty well with it, considering the cars only options were a transmission and color. A great interior, and build quality. It was more of a testing of the waters to see if there would be a market for Holden cars in the U.S. Appearantly it succeeded enough for GM to warrant to bring over the G8, as well as green light the GTO again for MY '10
No entry line engine (i.e. V6). And a starting price point of $33,000 is a bit steap for some coming from the Camaro/TA market who were used to $24,000 Z28’s.