It might be brazed, file a spot on it and see what color it is. I'm far from an expert but I've read brazing cast is easier then welding and when done right stronger then the cast itself.
If it were me i'd run over a few chuck holes at speed and if nothing happened I wouldn't give it a second thought. But then again having a back up axle lying around your shop is a sure fire way to make sure this one never breaks
