There's a great deal of Holden "art work" in the parts and service data that can be misleading--while a certain part may appear to be shown in an illustration, the reality is often not the same--so don't take it to heart if a printed illustration from GM/Holden & GMNA/Chevy shows an image that is seemingly "simpatico" for several variants, when in fact it's not.
As L77 mentioned--and I also remember seeing that picture--there's a PPV out there somewhere with the G8 rear panel (aka diffuser) fitted into place. I agree it's an acquired taste, and really may not be the best option, unless being different is that important to you. I actually have a GXP panel to play with, but I've never gotten around to seeing what it takes to make it work--your comments cause me to think it's not likely to be something I'd try. The Buick part is more interesting at this point.
Thanks BIll, I thought you might have something to add. I guess the reason that I'm confused is not simply that there was a possibly misleading picture of a part (in this case the valance), but rather that there are two distinct methods of installation and removal for these parts. Each of them show different bolt/pushpin mounting locations and methods. If I remember, I'll take a photo of the manual.
Regarding the PPV with the G8 diffuser, after closer inspection of the photo, I noticed that it hangs down at least an inch and is unattached toward the front. This is just as my test fit indicated. I wish I would have noticed this before I spent the cash on this spare diffuser. I do like the look though, if it actually fit.
As far as rebadging goes, if I had my wishes, I'd rebadge to the Australian Grange or the Middle Eastern Caprice SS!