Many West African immigrants work in the wholesale district that radiates from the corner of 26th Street and Broadway, yet there hasn't been a West African restaurant in the vicinity for years. Now debuts B & B, with Guinean proprietors, but serving the halal needs of a wide spectrum of Muslims. There's a better than average version of Senegalese cheb on the steam table-though you must assemble it yourself from stuffed fish, vegetables, and seasoned rice. Guinean food is ably represented with a sauce de feuilles, made with sweet potato leaves, to be spooned over rice. Then there are such diverse dishes as stewed lamb, couscous, mac and cheese, and fried chicken. All food is sold by the pound, and way-reasonable.