Prototyping technology is the way to go if you have access to the equipment. I'm pretty fortunate to have had access to these types of machines since the late 80's.
On my Carbon Car all of the parts I had to machine where first built on a rapid prototype machine to verify fit and function.
Currently my workplace we have 3 different types of machines.
A Dimension as seen on the Leno video, and a Fortus will build me ABS or Polycarbonate parts.
http://www.stratasys.com/
The third is called an Objet 350
http://www.objet.com/ Besides plastic parts it can make rubber as well. Can you say bumper grommets on demand?
While these are for plastics or rubber there are other machines that will build parts out of metals, epoxies, and even paper.
With the quotes I get for machining 1 or 2 parts it is way too high to have the design not work. The final parts are pretty strong. As an example after designing a T5 transmission mount with a polyurethane bushing in it I was able to install it in the car for fitting and left it holding the trasnmission for a few weeks while the "real" part was being machined from my verified 3D CAD files.
It was interesting that Leno mentioned the English cars as my 2 Triumphs have quite a few parts keeping them on the road with Rapid Prototype parts made over the years.
If I only had access to a scanner......
Later,
Richard