No, the grove diameter of a 8mm (~.323) is way to close to the bore diameter of a 338.(~.330) The "minimum" you need for a rebore is about .200 bigger in diameter. I would suggest going to a 35 Whelen...
There are way to many thigs to consider to make that kind of transition 8mmx57 to 338WM... The barrle could be junk to begin with, it may shoot ok now, but once you start tinkering with it you could have problems. I personally would never rebore a military barrel. There are way to many uncontrollable variables with the metal.
You would be far better off to rebarrel rather than rebore a M98, especially if you want to go to a mag. I would consider sending it off and getting it chambered for a 30-06 family case a 338-06 would be pretty close to 338wm velocitys and you won't have to modify the action.
Going from a "standard" length case and case head to a mag will require the action to be drastically modified, i.e. feed rails, bolt face, magazine box, follower etc, not to mention feeding and extracting problems...M98 weren't designed for mag length cartrages... You're looking at the least $400 worth of work, plus you would have to put a new barrle on so toss in another $400 for the barrle and work...and probably a new stock, there's another $100+ Now you got yourself a $150 dollar gun with 800-1000 dollars worth of work in it, and if you're lucky you sell it for $400!
You would be much better off going with a new rifle in 338wm if thats what you really want, save yourself some money and time... Gun doctors are about as speedy as taxidermists when it comes to working of stuff, expect at least 6 months+. If you have you heart set on a mauser type action, look at a Winchester, CZ, Ruger etc. You can pick up a Ruger 77MII at wally world for about $480...CZ's are just a little more and IMO are the best deal of the three.
Either way you look at it if you want to change a M98 you're going to drop about $400, and you will NEVER get your money out of it!
Good luck
Ivan