Sorry I feel compelled to add my 20c's.
I'm not sure about this HSV GTS mod but you'll find that many of the mods from smallblockhero are rips from other sims, particularly Forza.
They are complied to AC format then placeholder physics & sounds from default AC cars are used to complete a functioning mod.
In my mind it's hardly a true representation but each to their own I guess.
Also keep in mind KS did say they didn't want to see this type of modding & as such you won't see these on the official AC forums.