The pragmatic reasons for running away from this kind of build are many (and wisely adhered to). On the other hand, everyone should build a custom Mauser at least once in his life, if for no other reason than to punch that category on his Rifle Loony Card.
As mentioned above, COAL can be an issue with the '06 in a M98. In the one '06 I did there was no issue whatsoever but I've heard the stories. I think I would determine max length for cartridges to fit/feed in the magazine and have the barrel throated for that bullet and OAL, so as to avoid a couple headaches down the line. (In mine I may have gotten lucky in that regard as the first load I pulled out of thin air to try in it shot splendidly and feeds perfectly so I never messed around beyond that, and couldn't tell you what the throat dimensions are because if it works, who cares.)
