It Dan thanks for the info I had no idea that H&H was owned by South Africans. My main purpose for the rifle would be for African plains game so what you explained makes me want one even more. Thanks
Since you stated you were handloading for it, I suggest using something in the Hodgdon Extreme line. I shoot a .375 H&H Magnum and use Varget in all loads. It's stable in extreme temperatures so you won't get pressure spikes in hot weather like ball powders.
As far as i know remington didnt make any specific magnum lenght action. they make a short and a long action and the long action is long enough for the H&H. Ruger is the company that makes a short, long and magnum lenght actions.