You might want to consider getting a book called " The Mauser Bolt Actions" by Jerry Kuhnhausen. Brownells and Midway have it as well as some book stores.
It is the most complete book on Mausers that I have. M91 through M98' s

If your are going to buy just an action at a gun show etc. make sure whtt you are getting. There are some large rings that are drilled for small ring barrles.
The ones I have seen were unmarked.
There are a lot of good M48 and M48a' s out there and plenty of parts. They generally don' t have the pits that most of the more used Mausers have. They don' t take a cartridge the length of a 30-06 very well though.
Good luck