I know - I love lever actions - have 25-20, 25-35, 357, 44, 22, 32-20, 30-30, 38-55, 348, 360, 4570, 4590 etc to soon 475 & 50-110's. Nothing else has the feel. Followup shots if needed are much faster. And they are just more fun.
Beware - it is possible that you can not use a lever action everywhere in Africa. Check.
Brand new 45-90 winchesters on GB and Guns.com for a short rifle (24 inch barrel) are about $1400-1500. This is a good time to buy one - they are frequently very, very hard to find. Winchester must have made a production run of them recently. The short rifle is already drilled on the left side of the receiver so you can mount a turnbull base for a red dot sight. Saddle ring carbines are not pre-drilled so I would avoid those. I would prefer the 45-90 as a minimum for buffalo. Just my opinion. I would use a new winchester so you know you have good steel for higher pressure loads. The new ones are made by Miroku in Japan. And you can use it for a donor rifle later if you want a 475 or a 50-110 built (or buy another one)
Other gunsmiths will do a 50-110 conversion at less cost than turnbull and likely a faster turn around. Perhaps they would do a 475 turnbull as well or a 50 Alaskan. Starline has 50-110 brass and 50 Alaskan right now. However, Turnbull will return to you a lethal work of art - for which you will pay out of the nose.
If you dont reload, buffalo bore sells 45-90 350 gr. BARNES TSX-FN @ 2,350 fps
I just looked and see a 475 Turnbull on GB for $5,000. That is far less than having one built. And this one has a flat butt on the butt stock so it appears that it would be easy to install a recoil pad.
https://www.gunbroker.com/item/1121334792
However - Ruger guide guns or Africans in 375 or 416 can be had for ballpark $1200 new. I have both and they shoot great. They may not be as sexy as some, but the buffalo will not care.
groups from 375 and 416 ruger guide guns below at 100 yards. Lever action groups like the below are rare, partially due to iron or red dot sights with no scope magnification.
FWIW