Stalker:
I think the smart money is to have a very close look at the CZ 550 in .416 Rigby. This rifle is pretty-much DG shootable straight out of the box, and is probably much cheaper (and more reliable!) than having an M-98 worked up. Many posters here will contend that the .450-bore is significantly better than the .40-bore, but IMHO that is only true for the guide, not the client. A well-placed 400gr .416 premium bullet (..or two!) will do the job on buffalo very nicely indeed.

BTW, a well-stoked .416 Rigby will still recoil very stoutly in a light rifle, so keep the weight up over 10 lbs for comfortable shooting. It is far easier to teach yourself to enjoy CARRYING a 10-pound rifle, than it is to learn to SHOOT an 8-pound hard kicker!

JMHO...