Don't bother calling streetbeatcustoms!! That stuff is all B.S. and non of that crap works!!! Also you can call the andysautosports.com, but those kits are not specifically made for the G6!! You can buy any turbo and throw it on a G6 (within reason), but there are no kits custom designed for the G6!!!
Also if that is really the reason for the GTP stamp, it is kinda dumb cause the 90's GTP's didn't make 240hp!!! I don't think that is the reason, but I could be wrong!!