I welded mine with a small Miller welder, just turn it up to max and go slow, it will burn through it. If you want, you can try on some small scrap pieces and see if you like it. Mine did it perfect, but I wouldnt trust it on anything thicker than that. I also preheated mine as hot as I could get it to help. May or may not help.
My frame rail looks like that, but its from pulling on it when I got it stuck. Which, probably same as me, is what happened to yours (unless it had front end damage). I had to run a strap behind the leaf spring mount and pull on the actual spring bolt after I ripped both my hooks off. I ended up having to cut a new poly body mount down to level the frontend and fix the fender to door gap. No big huge deal.