When I had to repair my backhoe because the top swing mount ripped off and the bottom 1 1/2" plate bent, I ended up having to grind a bevel in the 1 1/2" plate so I could straighten it. In talking to people experienced with repairs on heavy plate, they suggested against using braces to hold everything from moving. If the piece is restrained from moving actually causes internal stresses from the heat and not being able to expand and contract. I left the plate bend down about 10 deg. and the heat pulled it up a little more than needed. My friend brought his truck out and we used a rosebud to heat it up and pull it into the right position. Some weldments can be clamped to prevent movement but not this type of application. Preheat and peening isn't a bad idea either, just don't beat the crap out of it trying to peen it. That will add stress as well. Looks like it was a pretty good repair though.