welding a fireplace grate?

I broke my manifold on my kubota. While engine was still hot i welded it back on. Ground a vee and went to town with the mig. I started tractor while it was still hot and its still fine.
Not pretty.
Propane is hot enough for pre-post heat.
Weld a couple bolts across the joints, may give it some strength.
Whats the worst that could happen?
Have welded a few cast pieces, sometimes a couple attempts to get it to hold.