How-do, Flintman!
That large-ring M98 Mauser action came in several minor variations made in more than a dozen countries by dozens of arsenals. It would help if you posted the manufacturer's markings to determine exactly which action it is.
Typically, the large-ring M98 was originally made for the military 7x57mm, 8x57mm, 7.65x53mm, and .30-06. rounds. You can get an idea of action suitability by comparing .375 H&H to an 8x57mm drawings. MORE suitable would be any of the short Magnums made for standard-sized actions (6.5 Rem, 7mm Rem, 300 Win, etc) and any of the standard rounds using a .30-06 headsize of .473" diameter (.22-250, 243 W, 6mm Rem, .257 Roberts, .25-06, 6.5x55, .270, 7mm Rem, 7mm-308, .308, .35 Rem, etc). You get the idea. Most of these require minimum feed rail & ramp mods, and no bolt face & extractor mods.
YES, you can re-barrel to .375 H&H Magnum, but the action is not long enough to magazine feed factory rounds. The factory Magnum 98 actions were about 1/2" longer than the standard M98.
It needs considerable modifications to the feed rails, bolt face, extractor, magazine box, feed ramp in addition to the usual drill & tap for scope mount, low-forging of bolt handle, polish & blue. The action length will also limit you to COL and type of bullet and of course, seating depth. Use of cast bullets will remove all action strength worrries.
Also, depending on how your .375 H&H chamber was cut, you may simply fit to action with some lathe turning, or you may need a chambering reamer.
None of these are technically difficult, but the lengthening of mag box and feed ramp are very time-consuming with hand tools. Bolt-face work will require a lathe or mill.
HTH
John
