I don't think American cities track their religious populations. Last I saw, Muslims made up 1% of the black population of the US. I bet it is slightly higher in Detroit, given that this is the birthplace of the nation.

I know one African-American [[not of immigrant stock) Muslim, though I don't know if he is the Nation or not. He has an affinity for Farrakhan, so probably. He seems pretty into black nationalism, and if anything hates Jews. Charming.