Clean all the paint off the bellhousing for at least 2 inches (50 MM) around the crack, then drill and tap the broken piece sideways between the two bolt holes for a 6 MM bolt to hold it in the proper position, aligning the crack exactly. It might be a good idea to clamp the piece in place around two short bolts to be sure the thread pitch is right. Then use an acetyline torch and a flux-coated brass welding rod to reattach the broken piece. Build up the brass repair 6-8 MM thick all around the bottom and sides to reinforce the broken spot. Next time, be sure the bolts don't bottom out in the holes, which is probably what broke it in the first place. If you need to re-tap the bolt holes due to misalignment of the threads, the size is 1/2"-13.
Jerry
