I love this video, seen it quite often... I believe it's one huge turbo, although I could be wrong. I say that because they're a definite point where the turbos kick in, rather than a smoother output like there would be with dualies.
Moss, look closer at the video, in the first run there's only one strap holding the car in the rear, on the second run there are two. First time through there would've been some major carnage if the dyno hadn't been shut down!!

Oh yeah almost forgot, I've got over 2 gigs of racing/car related videos... if someone wants to host them I'd be happy to share some of the cooler ones!