I have the opportunity to buy a set of 18" Turbo Twist wheels off a 2004 C4S. They're in great condition and I can pick up for a reasonable price. The specs are 18x11 ET 45 for the rears and 18x8 ET50 for the fronts, so I'm pretty sure the the fitment will work on my 997.1 Turbo.

I'm wondering if these hollow spoke. lightweight wheels (confirmed via part numbers) work well as track wheels? Is anyone using them?

Sure, turbo twists make great track wheels. My experience is with 996tt, but had the 997TT rotors. Clearance is tight-I can’t speak to caliper clearance on a 997. The hollow spokes are light and robust. No doubts as to whether the wheels are up to track duty as with some 3rd party. Of course they will fatigue like any other and need checking before & after. That they are easy to clean up is a bonus. Put some NT-01s on and you’ve got a great track setup. 315s require spacers else they rub the inner fender liners at the track.

Not sure if the 997 front diff needs a certain size to work properly but the twist wheels are tough and OK on the weight.

I've used them as track wheels for a number of years on my 996 tt with no problems.

best setup ever for stock twists for the track is, as jayzbird noted above -
7x15 spacers with 315/30/18's and fenders rolled on lowering spring or coilovers. perfectly capable for the weekend track.

I use them as track wheels mounted with slicks. Will probably get some new ones this year so I can go wider (9 and 12), but they do work well for sure. Cheap, easy to clean, strong, and they came free with the car...what's not to like (besides they're a bit narrow)??