You will not get that straight with a sledgehammer or a 10 ton porta power. It may only be 5/16" thick (just a guess) but it is the dimension of the rail and the flange that give the rail its strength. I highly do not recommend redneck backyard engineering of stuff like that. You heat that rail and you'll take the temper out of it. Sure frames can be welded but that is exactly why they install a reinforcing sleeve in there. I would take it right to a professional. They have jacks and presses good for 100+ tons that can cold bend that straight like nothing.
In my 30 + years of being in the shop and also as a driver I really don’t see a big problem with straightening the bends in the rail with a porta power and possibly some held from a sledge.
We have actually done these kind of repairs many times over the years with a zero come back and failure rate.
If the rail was bent forward of the rear axel housing mount I might have a different opinion but that would be on a case by case basis.
I will say our shop has proven to be very successful over the years by being honest and not up selling services or parts that company’s don’t need and especially not useing the famous scare tactics that you could kill someone if you don’t spend the money to repair it right.
In full disclosure there have been some instances over the years where I had to have the infamous
“You could possibly kill someone conversation “ but in my opinion this is not one of them.