Personally, I would have no quams of shooting a 98 that had been opened up to shoot the .375 H&H with factory or factory equivalent loads.
: My only 'problem' with this practise, is that with metal removed from behind the lower locking lug, there is a margin of strength reduced.
: With today's 'penchant' for loading to the limits, there is a real possibility of overstepping the strength boudaries of the action, in the form of stretching behind the lower lug.
: Kept to factory-equivalent loads, which provide and have provided more than enough power over the years, an opened action, if done by a qualified gun-smith will provide all the strength necessary. Afterall, look at the many rifles Rigby and other makers who've done just that with Mark X Mauser and 98 Mauser-type actions over the years. they worked well years ago, and still do today.
: Just such a rifle will provide .375 power, in a shorter action and lighter rifle of 8 to 9 1/2lbs.- whatever is desired. Personally, I prefer 9 1/2lbs. with scope, and 8 1/2lbs without.
: If you are already a wildcatter, there is an alternative in the 9.5X68 which uses the 8X68S case and requires no acton alteration other than the bolt opened for magnum rims. The one I made up back in the 80's was on a CZ24 military action with magnum bolt face. Huntingtons now makes the dies for this round. We had Huntington's make up dies. This 2.620" long case duplicates the .375's capacity and actually will give slightly higher velcocities than the factory printed loads suggest. RWS brass is stronger than American brass by a considerable margin.
: Brass can also be made from .300 Win. Mag. and .375H&H brass by turning the belt to .522", trim to length if necessary after opening up the neck or pushing back the shoulder, whichever is needed for the brass used. The shoulder is properly located for headspacing during the forming operation as it is a rimless case and needs a shoulder for proper headspacing. The brass easily expands to proper size ahead of the belt and will take any loads equivalent to the H&H just fine, without any safety problems. Once FireFormed, the capacity is the same as WW .375H&H brass.