"Does anyone have thoughts on where the spoiler and diffuser in the attached might have originated - regular aftermarket or custom piece? I know it would be too narrow for a ZR-1 as it sits on this regular C4."
The spoiler and rear diffuser in the picture are renderings and not actual products.
If you're going to put a rear spoiler on your car, this is one of the better looking ones.
The original link is here if you want more info:
http://www.corvetteforum.com/forums/...-opinions.html