You'd need an early POD if you want a Nigeria Wank.
I suggest you go with both Northern and Southern Cameroon acceding to Nigeria in 1961 instead of just the North acceding to Nigeria. This gives Southern Nigerians more power in the republic and so the 1966 coup d'état never happens by disaffected southern soldiers, and so there's no counter coup by northern soldiers either, and the entire Nigerian civil war is butterflied away. Plus they get more land and oil.
So no war, and by the current year Nigeria has a strong, uninterrupted tradition of democracy. This stability would give you the Nigeria that your asking for here.