Standard length action vs. longer actions, ie .375h&h?
Less you're modifying an older action/rifle, who cares? many rifle makers chamber the .375H&H so whats the matter if its a longer action?
The idea is that there are greater clearances for feeding and ejecting rounds which should improve feeding reliability. As you can tell from my last posts I would have no reservations with the 70 pre 64, or the classic action. In fact if you do asearch on "dangerous game rifle" you will see the 70 mentioned over and over again in various magazine articles as a good action for that purpose.