Works on Impalas!
Ok Abrasive, good news! It fit my 2004 Impala perfect, and I took a picture of the parts description for the cover, so for two part covers, if the part numbers match, then it will work.
Before I did any work
Picture with the cover removed
The cover itself - looks a lot like the GP cover
Cover part number from my Impala - note GRAND PRIX imprinted, so GPs probably use the same and thus anything using this part works
New deflector in place
Picture of the finger guide, where it should be
Trimmed the rubber and plastic piece from the bottom of the cover
Everything back together
I'll be sure to pimp this out if I do make it to the New Jersey NAOIA meet and greet next weekend. I've got some more pictures, but they are just different angles of what I already took. The current write up is good, and Impala can be added to the list of cars this works in! I don't remember if my 2000 Impala had a one or two piece cover, but if you have a two piece, it's a given it works if you have the part with the numbers I gave above.