Hi Colin,
I should preface by saying this is far out of my area of specialty - but I'll give it a shot!
The scabbard I thought could be later because a) the material is in great shape, no small feat for a tribal weapon in probably less than optimal storage conditions, b) the simplicity of the design. Even the work from Cameroon (I imagine you are thinking of Tikar scabbards?) is usually well formed, your scabbard strikes me as slightly crude on the bottom chape, no offense meant by that observation of course. Given that the sword is clearly Mandingo and corresponds to a type we have some records on and since the Mandingo are not, to my knowledge found in large numbers in Cameroon I'm fairly confident the sword is not from there.
That said, I don't know really if the scabbard is later or older. It may just be very well preserved! It was more or less a guess based on the rather basic design and fittings and the fact that older pieces seem, from what I can tell in photos, to have had more elaborate fittings and leather molding. So it was more or less a guess since it didn't match up with the examples I knew of collected in the early 1900s. So short answer, I don't really know.
The blade... very hard to say unless I have it in hand. I'm not even 100% always sure with takouba. I tend to assume though that anything I am unsure about is native. Native blades seem to usually have a lower carbon content and less flex. My guess is a soft blade was considered preferable to a brittle blade failure. Is the blade single edged? The placement of the fullers reminds me of export blades for nimchas from Italy (not centered on the blade, but higher). But I would then expect a more substantial spine. So my best guess is good native work.
So in summary, I am suspicious of the scabbard mainly because it doesn't confirm to the normal examples, but I have nothing firm to go on to indicate it is not "old". The blade is obviously quality workmanship but I don't immediately recognize a known European pattern - hopefully those more in the know will chime in at this point. Sadly my studies have been in such a narrow field I tend to get out of my depth quickly in other topics!
Cheers,
Iain