The GTS-R was a full-blown race car, straight from the factory. It had minor things in common with the production car. Here are a couple pix I took of the Brookspeed GTS-R after it's big wreck at Road Atlanta back in 2002. You can see how different things are under the skin. Also even just this one shot of the roof area of the American Viper Racing GTS-R makes evident a number of differences (ventilation, windows, etc).
And as long as I'm posting pix, here's a couple shots from the GTS-R tent in 2001 before the screwheads at Chrysler abandoned their customers with the deepest pockets. (Note the ventilated hood in the first picture.)
He probably really meant the GT2/ACR. Also, the ACR did NOT come with a 10qt oil pan. That was a standard change in 00 I think.
The GT2 was mostly cosmetic add-ons to make it look a bit like the GTS-Rs that were kicking ass in LeMans. It was a commemorative car (100 made). The ACR came out afterwards and was meant for "club racing". Major points are an adjustable suspension, different spring rates, bbs wheels, 5 point harnesses.