A ton of work that may be totally unnecessary.
If rust is the reason it broke then replacing the whole crossmember may be the best option. But if it just broke because of a poor weld, which is very possible, then there’s absolutely no reason to replace the whole crossmember.
If it was a poor factory weld you should have no problem welding the anchor back into place and gusseting it. And then you can gusset the other side to match and be on your way. I gusset the torsion bar anchors on all of my cars regardless, it goes right along with seam welding and gusseting the K frame. Some of the factory welds on these cars are terrible.