I am a lefty and I want to get into the big bore guns and I was wondering what would be my best options for a left-handed big bore.

I know that they make a model 70 lefty in 375 H&H which I want one of those, but to get anything bigger than a 375 in a lefty I think you have to get one from their custom shop. Is their a better option? or shoud I just buy a second 375 lefty and rebarrel it for a larger caliber based on the 375 case??
I am mostly just going to be using these for fun and to make my hunting more interesting but I do plan to go to Africa one day but I don't know when..\
Also on the same token what would be the best barrel length, weight etc for a dangerous game rifle that will hopefully see Africa one of these days?
Any suggestions would be greatly appreciated..