I figured I would revisit this topic after consulting "The Mauser Bolt Actions, M91 Through M98, A Shop Manual" by Jerry Kuhnhausen and on page 161 he states:
Inspect M91~M96 Barrel Torque Shoulder
M91~M96 receiver have only a single external barrel torque shoulder. This shoulder surface also must be square and at 90° to receiver/barrel centerline. See figure 191.
Barrel torque shoulders can be recut and trued on a one time basis subject to the following limitations:
1. Not more than .020" must be removed from the torque shoulder. <--- (the information I was looking for)
2. At least 6 1/2 full barrel threads must be left in the receiver.
Carefully inspect receivers before shoulder adjustment. If surface pitting or damage can't be cleaned up within the above limits, do not use the receiver.
There are also some general criteria listed on what makes a suitable receiver for sporterizing. Too many to list. But as far as knowledge goes, from what I gather, this is the bible when it comes to mauser gunsmithing.