No need to mess with the welds, they are stronger than the rest of it. If you can heat it and bend it back, you should be good to go. Vee out the cracks, and then weld those up, full penetration. You might even add some plate reinforcement after that, that would ensure it's stronger than new. Not absolutely necessary tho. I would use a come along to pull it straight, heat, crank, heat crank. Stick welding would be better because of the rust, mig would be prone to porosity, and probably doesn't have the heat input to penetrate deep enough on that thick of metal. 7018 if you got it, more ductile.
When you are done welding, double check the straighteness of the connecting angles, and maybe tweek them after it's all welded up if need be.
When you are done welding, double check the straighteness of the connecting angles, and maybe tweek them after it's all welded up if need be.