And that's exactly the problem with 20" wheels on an A-body in my books: The wheelwells are so small compared to modern cars that the wheels look larger. So you don't really need HUGE wheels to look like you've got huge wheels; 18" wheels and tires on an A-body look pretty big. You'd have to run very low profiles to get 20" wheels to fit. But it can be done with the right tires and backspacing.
That green Demon looks pretty mean as it is, like it's ready for a track day.