First off, it is not a sporterized military Mauser, it is a commercial FN M98 action chambered in a Weatherby caliber. Weatherby did use FN actions in their earliest rifles.
Buehler made scope mounts as well as the low swing safety on the rifle. Their scope bases and rings are now hard to find, the low swing safetis not.
The checkering alone on the stock would cost over $1200 in today's market, and the piece of Claro used for the stock is also very nice, but neither are in a recognizable Weatherby pattern. Value of the rifle on today's amrket is probably close to $2000. As to whether or not Roy Weatherby made the rifle himself, it would be impossible to guess.
If it is actually a Weatherby rifle, it will be marked Weatherby in the chamber area. Roy Weatherby's trademarks were the Weatherby name in script, and a diamond in the grip cap. That rifle does not have a diamond inlay in the grip cap. That does not mean that it is not in fact a Weatherby rifle, but it reduces the likelihood.
In summary, unless you have a letter or markings on the rifle that could show provenance or that Weatherby did indeed make that rifle, I would call it a case of mistaken identity. If I were to guess the vintage of that rifle, I would say it was made in the 1970s or 1980s.