I hope no one was planning to get the aluminum glowing in order to straighten it out. From my experience, aluminum isn't like steel or iron that glows long before it melts. I have melted and cast aluminum before and from my experience, it basically melts before it glows. I don't think heating it up to 500-700 degrees would hurt when trying to straighten it out, but I also don't think it is necessary. Like I said before, I have straightened three or for fire boxes over the last couple years with no heat. Just simply putting the box on its back and apply my weight at various points across the front of the fire box. Takes just a few minutes and if you use a yard stick, you can measure how straight it is as you proceed in straightening it. Of course, if you don't want to remove the fire box from the frame, bar clamps are probably the way to go. Again, no real need for any heat IMO.