The sleeve method of repair I mentioned would be a split one. Two halves to sandwich the stay. This way the stay won't have to be cut! The sleeve's ends could be shaped to an aesthetic that the rest of the bike suggested. I agree with Pete in the balancing of the look, a sleeve on each stay. Before the current bridge is cut away I'd measure the axle to brake hole and modify it as i saw fit. To center the pads in the caliper's slots or to add more fender clearance. Of course steel, 4130 would be first choice, would be used. I'd also address the crack with a pair of end holes. Bronze/brass would be the filler of my choice. Any other frame mods in the area (like rack mounts or brake cable stops) should be considered at the same time. Andy.