time to break out the books
Off hand, I cannot give you exact info, as my references are about 15 miles from me, but I can give you generalizations and suggestions.
When talking about Mausers, I'm sure you understand that they were making them in all sorts of different versions and from different factories for quite some time. There had to be variations in the materials used and in the heat treating processes that were utilized.
Jerry Kuhnhausen's Mauser books gives a fairly concise history and explanation about nearly all these different variations. He will tell you which ones to look for, and which ones to avoid. This is in case you were thinking about modifying an existing action. I wouldn't recommend this though, as unless you have lots (years) of experience in heat treating metals and have access to the various different methods for heat treatment, you are playing with a jug of dynimite. Heat treating a Rifle receiver isn't something you can do with a propane torch!
A look into my Brownells catalog show that Dakota Arms makes their actions out of 4140 stainless. This goes for every action they have listed from their pre-'64 Model 70 copy to their #10 single shot. Smiths Industries M14 receiver is cast from 8620 steel, and Meacham's Hi-wall copy is also made from 8620 steel (CNC machined) in is case hardened.
I would say that which type of steel you choose would be dependant on a couple of criteria; namely tooling, availability of material, and experience. Keep in mind that whatever you end up with, it will have to be heat treated, and this (again) brings into question what your resources are.
Quite a daunting endeavour your are taking on. I wish you luck, but caution you to do your homework and get advice and directions from those who've already been down this road, folks such as engineers at Winchester, Remington, Ruger, Dakota, etc.
Good luck, and don't blow yourself up!
Unkel Gilbey