Hi Tim,
I've really been intrigued by this piece and have gone through as much as I can find on Cameroon weapons. Its been a truly fascinating adventure! From what I can find in previous posts and threads, there are indeed arm daggers somewhat similar to this that you noted were South Saharan, and in the weapons of Cameroon there seem to be wide variations.
Going by what I have read, I would presume your piece might be a tebu/tabu hilt mounted with a sword blade, therefore an arm dagger hilt. Naturally I dont think this would be worn on the arm with a 33" blade, but the reworked scabbard retains its arm loop. The blade and wrapwork on the hilt to me suggest possibly Bali tribal group, but I am uncertain if that would concur with the Mandara attribution you note.
The debate on the diffusion of weapon forms and blades throughout Africa has been going on for a very long time. The key to most of this is to focus on trade route networks, colonial incursion and nomadic movement /interaction. It is really not unusual to see weapons vast distances from thier origins in Africa, and I've always enjoyed the challenge of trying to trace some of these movements.
Very nice acquisition Tim! and a great study piece!!!
All best regards,
Jim