Make sure its nonlock-up, or lock-up, depending on what you have, and also, earlier 350's had thrust washers at the pump and back of the case. The later ones use torrington bearings. If same-same is not used you will end up with too much, or too little endplay. Is it just the bell housing that is cracked?? If so, and you have the other piece, a good welder can weld it back on.