RT2506 mentioned that the Yugo large ring '98 is shorter than a standard '98 large ring. They should work fine on cartridges that are shorter than a .30-06 and that have .473" case heads, I wouldn't use one for a magnum cartridge or any modern high pressure cartridge that is designed for more than 55kpsi. No sense in pushing your luck.
On metallurgy: I always thought the Mausers were through-hardened receivers and bolts. However, Parker Ackley has some info in one of his handbooks that states they are low to medium carbon forgings that are case hardened up to depths of .015" as shortgrass said. The case hardening must be for wear resistance, since the core metal has to have the strength and toughness to contain the chamber pressure spikes without yielding. The thin case hardened surface is very strong, but is so hard it can be brittle. It must be supported by the tougher (softer) core of the forging. Steels with 25 to 45 parts carbon (.25 - .45 %) will respond to quenching from case hardening temperatures. The higher the carbon content, the higher the hardness (strength) will be after quench. Unlike the carbon rich surface, they won't get hard enough to be brittle if the heat treat is done correctly. I don't know if Mauser or Zastava does a low draw after quenching, and Ackley didn't say either, but it would make sense to me to relax some of the peak stresses caused by the quench.
My impression is that the post-war Yugo's and Zastava commercial Mausers (Mark X, Charles Daly, Whitworth) are good metallurgy, properly heat treated actions. No proof other than examining several of the MK X's and Whitworths that were massively over-pressured. Blown primers, stuck cases, gas cut bolt faces, etc. All had been chambered in modern belted magnum calibers. I don't have that experience with the 48's, but I already said I wouldn't chamber one in a Magnum caliber. The .473" diameter cartridges leave more barrel steel in the chamber than the magnum cases. Just extra insurance.
I've drilled and tapped several large ring and small ring Mausers and one Yugo 48A. For whatever reason, none were a problem like the U.S. 1903-A3's that I've drilled and tapped, which were nothing but trouble. They and Garands and M-14's are all case hardened and the surfaces will turn a highspeed drill instantly. None of the Mausers have done that so far. The case is not as hard, or it's much thinner, or both.
Truing the face and inner shoulder of the barrel seat won't hurt because they are not wear surfaces, and should only take .001" to .005" to clean up anyway. Bolt lug faces and recesses are wear surfaces, but should only require .001" or less to bring into 75% contact. I would do the barrel seat faces for sure, but lap the bolt lugs only if they need it (less than 75% contact).
The Mauser actions have an ace in the hole. A 3rd safety lug. I've never personally seen one catch a bolt, but I like that it's there.
Shortgrass makes a good point about liability. He has to set limits on things he's willing to do. To a lesser extent though, so does a hobbyist. For instance, I wouldn't touch anyone else's trigger, even to increase sear engagement or spring load. Too much liability for a hobbyist.
Brownell's sells some very plain walnut sporter stocks made by "Wood Plus" for Yugo Mausers. Check them out.
Hope this helps too. Good thread.
Tom