The right side of the stock where the tang is cut out does not leave me to believe it is for a Mauser 98. That tang area should extend further up.
Also there's a cut out where the trigger group and the magazine is. That wouldn't be necessary on a Mauser (unless perhaps it was mean for some sort of detachable box magazine version).
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!