All these "found in the wild" WWII restorations are exactly that. I would bet that this Spitfire has less than 20% of it's original content in it and less than 50% of original WWII Spitfire parts in it. Just how it goes. Most all of the WWII planes that are 100% original don't fly and are in museums.
They say that P-51 Mustang builds are so common that if you were to combine all the various talents around the world, you could easily set up a factory building 100% brand new Mustang airframes exactly to WWII Mil spec.