.300H&H will require removal of lug metal, seems to me. I would not go that way.

The .30 x 68mm would fit in the action with the good barrel & give you about the same capacity as the standard .375H&H. In performance, it should be about the same as the .300 WTBY & sort of your own case, rimless .300 WTBY.

Hell of a performer.

Not only that, if you wanted, you could turn the belts on mag cases down to .324" neck, trim to length and fire form - done
or you could use 6.5x68 or 8x68 RWS brass.