Again, I think in your double you are limiting yourself by chambering for short-cased cartridges designed for lever guns, which to achieve dangerous game stopping potential would have to be loaded to higher pressures than what will be safe in your DR. I don't question the potential of these rounds in the right actions; I own levers in .348 WIN, .45-70 and .50-110 WIN myself. The full length .50-110 case has even more capacity than the .50 Alaskan, which like the .450 AK uses a blown-out .348, which itself is essentially a trimmed back, tapered .50-110. +P loads with modern powders in these calibers really rock. It's just that in a DR you are limited to lower pressure, but not in cartridge overall length.

With your CUP limitation you may want to chamber in .45-120 and handload. The 3 1/4 inch case length will give you more capacity to achieve higher energy levels with less pressure. You're not going to be able to use factory loads anyway unless you use milder .45-70 ammo safe for trapdoor Springfields. An action strong enough to handle up to just 40,000 or so CUP would give you so much more potential.

How far along is this project and how much is it going to cost? You don't have to answer that question, but as much as I love custom guns myself, just keep the Baikal as a 20 bore bird gun, buy a Sabatti .470 NE for $5K, have your gunsmith check it out/fine tune it, and be done with it. Coupled with the 9.3x74R you will have a great two gun battery for Africa! No concerns about having enough gun for any situation.