What facet of gunsmithing are you interested in?
Like I said in your other thread, the Kuhnhausen shop manuals are tough to beat for the best information.
I own many gunsmithing books...some of them aren't good for anything but ideas, others contain good information if you have a basic understanding first.
The Roy Dunlop book is a good recommendation.
Patrick Sweeney has a book on gunsmithing for rifles that isn't bad. But it's heavy on pictures and kind of light on information, IMO.
If you're looking for info about customizing that Mauser, the AGI video that deals with the subject is not bad at all.
Edit: Had to go answer the phone, and you'd already posted again before I got back.
For .223, you will have to weld up the bolt face. That's not something you're going to learn how to do in a book. You'll likely need to make some rail and feedramp mods, as well. Again, experience and mistakes will be your professors.
Just my recommendation, but I'd choose a less ambitious conversion for your first project.