It will not work as the 300 H&H is more tapered than the 300 Win Mag. You would also have to be sure the Win M70 could accommodate the longer 300 H&H round. If so, then you could make a 300 H&H Improved which would be something like an 8mm Rem Mag necked down to .308". There is probably a named wildcat cartridge that matches such a configuration, 300 Ackley Long or 300 Ackley Magnum? Or there is the 300 Weatherby Magnum.