I resent the notion that Chad is West African. The people in the South are Central Sudanic -- just like the tribes in South Sudan's Raja county. The other tribes are the same tribes in Darfur -- like the Masalit and Zaghawa.
The Arab Ta'isha-Habbaniya and the Misseriya also reside in Darfur and Kordofan. Chad is essentially an extension of Sudan.