I know that rifle personally, and it isn't the first No4 Savage to be seen, without lend lease markings. The serial number, is in the proper range and all of the rest of the stamps, are authentic. The receiver is untouched and original. It certainly isn't a one off, although I do admit they aren't frequently encountered. It's a very clean rifle.
I've heard a similar rumor, but was informed by a deceased friend, that was a WWII REME, that just wan't true. The rifle, came from "Tiny" Tim Ryan's estate and Wheaty can vouch for the validity of his credentials.