Before converting the old mauser actions to higher pressure cartridges, the should be checked for cracks (flux and x-ray). Then machine work done, and finally complete retemper of the action and bolt. This retempering is usually beyond most smiths equipment but there are places that the action can be sent.
I have, just for fun over the last 46 years, sporterized ~ 100 Mausers mostly built either at Oberndorf Germany 1903 -1906 or in Brno Czechoslovakia1924 - 1942.
I would be really angry if some sent them off for heat treat.
It astounds me that Keuhnausen could write a book as good as "Double Action Colt Revolvers" and also write a book as bad as "The Mauser M91 through M98 Bolt Actions. A Shop Manual"
The Mausers book is filled with misinformation about things like heat treating, lack of drawings for tooling described, is disorganized, and un edited.
There was a chief engineer Walsh who, as a hobby, collected and sporterized Mausers. He wrote a book:
Reading Walsh's only book, I interpret it as an attempt to fix the mess that Kuhnhausen left behind.
I have spent ~35 years of my life as an engineer designing things and communicating technical information. I see no excuse for the Keuhnausen book being published.