From what I've seen it doesn't seem like its all that big. I know while doing some research I stumbled across a Corvette forum post where a guy just used the brackets where his charcoal canister use to be. Also, saw something on one of the car shows on velocity where they used a Holley version of the same system. It tucked away nicely on the car they were working on.
With that said I would like to see where guys are installing these on A-Bodies