Not sure if they're re-doing any work but back in 2008 the NYT (as probably many other news outlets) reported on the restoration as:
The final product, which the studio is calling “The Godfather: The Coppola Restoration,” combines bits and pieces of film recovered from innumerable sources, scanned at high resolution and then retouched frame by frame to remove dirt and scratches. The color was brought back to its original values by comparing it with first-generation release prints and by extensive consultation with Gordon Willis, who shot all three films, and Allen Daviau, a cinematographer (“E.T.”) who is also a leading historian of photographic technology.
The tight grain of the image, so important a component of Mr. Willis’s original low-light photography, has returned to particularly spectacular effect in the four-disc Blu-ray edition. The effect is not unlike that of a pristine 35-millimeter print projected in perfect focus — a rare enough phenomenon in a movie theater and, until quite recently, inconceivable in the living room.
To be fair, the source material makes the first two near impossible to get to a crystal clear standard. I have the Japan only Coppola Restoration Box Set, and the films are a marked improvement on the previous releases, but I’m picking the best a 4K transfer will do is clean up the currently pixelated blacks.
That said, any good improvement can only be a good thing for these masterpieces.