http://pontiactransamshakers.homestead.com/ (this is also the same guy on got some of my parts from)
It's an aftermarket kit to make the later shakers funtional like the 70-72 shakers. It operates via a switch mounted at the pedal. From 73-76 they had a removable blockoff plate, but all 77-81 shakers were purly cosmetic.
When I did the swap, there was two rules - it must be mounted to the breather (not the hood), and it must be a functional air intake. Even though they were common place on many muscle cars, I hate fake scoops/vents/etc. It doesn't take that much more work to make things functional - fake is just extremely cheesy IMO
I don't really have any good shots, but these few kind of show the flap that replaced the fake vents at the rear of a stock 77-81 shaker.
http://www.motortopia.com/files/74/album_exterior/449b536b2e6d9/100_0570JPG_Thumbnail1.jpg
http://www.motortopia.com/files/cars/album_exteriorinterior/47e5334d457b1/100_0654jpg_Thumbnail1.jpg
http://www.motortopia.com/files/cars/album_exteriorinterior/4776d7071acdd/100_0624jpg_Thumbnail1.jpg