There can always be 'issues' when you remove metal that helps support the lower locking abutment. That said, early case hardened commercial version of Mauser '98s had/has an inside mag length of 3.4". The military mag box of a std. length '98 is 3.315". That says that .075" was removed, and from the front. Newer commercial '98s are made of better steel and heat treated better, I have a Springfield '03A1 box in front of me and the thickness of the front wall measures .080" thick. It could be removed and a new front wall welded in, extending the inside length of the box. This not a recommendation to do this 'lengthening', but that is how it has been done in the past. If I convert a military Mauser '98 to use a commercial mag box/trigger guard assembly, I use a 7/16" carbide end mill and finish dressing by hand, with a file and wet & dry paper wrapped around a wooden dowel to polish.