The challenge is to have the Ashanti empire undergo a industrial revolution. I see the Ashanti as most likely due to similarily to the Japanese not being that far behind Europe. Perhaps the Ashanti were able to fend off the british in the first anglo ashanti war?(1826-1831. British seem to mostly only have won due to superior artillery as the Ashanti army was completly armed in flintlock muskets.) That would allow them not only to keep their coast but also they would get a sight of innovations going on in Europe. This could cause the Ashanti to go to possibly the Dutch(they often sent royalty to European colleges and were allies with the Dutch) for help in Modernisation. This could also encourage them to strengthen centralisation to keep the Fante under control,and make them focus on internal development because at the time they were constantly warring with neighboring kingdoms. If the Ashanti modernise and keep their eye on europe and the industrial revolution which wasnt completly in fruition yet along with remaining up to date with weapons doesnt seem like a far cry that they'd industrialise when the industrial revolution was in full swing.(The Ashanti would have large amounts of Steel albeit importing coal,but outside of producing it minorly in some areas Japan imported coal too). Or atleast thats 1 idea.