Is this possible? I have an old Bell and Howell 240 which was designed to shoot regular. However, would super16 work on it? Is there some kind of adaptor?

Super 16 is single perf film, so it would probably take significant modification to a standard 16mm camera to make use of it. Although, if you were lucky and your camera only had a registration pin on one side, then I suppose you might be able to just change the film gate to the super 16 format.

However, since you're talking about shooting on film and finishing digitally, I still believe there's no reason you can't crop regular 16 to a 16:9 image... The film has more resolution than the digital transfer will anyway.

Here, this might help: http://www.visualproducts.com/productInfoProductDetail01.asp?productID=524&Cat=96