I don't see why you couldn't just plate that and weld tabs on, but I'm not a fab guy. I'll ask an expert....
@kennythewelder
You have to get all of the crack out, or it will crack again. You can drill the ends of the crack, grind out the crack, and fill wild this. Adding steel is usually a good idea, but, if the metal is cracked, it's probably stressed, and if it's stressed, that changes the integrity of the metal. Really, your best bet to is to replace the mounting bracket. My right rear shock mount bracket worked it's way loose. It was factory rivited. I centered it up on the frame, and welded it in place. This was several years ago go, and it's been good since. You could always get a new bracket form the junk yard.
