Thank you all for your assistance. I'll take a look this weekend, and if I find any other markings I'll post here. Otherwise, we'll stick to the 8mm rounds made for the 8mm, and the brass / bullets he has already.
I'm assuming that since he has the 98 Mauser action that it can handle a bit more than the 88 (though at this point I doubt he'll go through the supply he has already made up in his lifetime. He doesn't fire it much).
Thank you again!