Well, not exactly. This was way too much work. It's probably easier to purchase a replacement crossover! Anyways, I wanted to see if it could be done.
-Build up the broken corner with an aluminum welder. Tape off the rest of the faceplate. Aluminum welding splatters and will damage any aluminum the splatter lands on, especially the raised aluminum trim around the face of the crossover.
-File the corner to proper size. Both corners, front and back. Build up with the welder if you have low spots and file again.
-Coat the new corner with Bondo (automotive body filler) and sand smooth.
-Put a faceplate with good corners over your repaired faceplate (Face to face), clamp together and drill out the holes on a drill press. This needs to be dead perfect. The holes, after countersinked, are very close to the edges. If you're off, when it comes time to countersink, you'll go right off the edge.
-Countersink the new hole to match the existing.
-Paint the repaired area.
Sounds easy, huh? I had a handful of faces with broken corners, it was this or toss them out! This was more successful than the autoformers I tried to wind