I can't see which way things need to go and how much..... but here is a general option. When I say tree, I mean anything unmovable. But a tree is many times a good place.
Chain truck frame to a tree. use a come-a-long, winch, trucker ratchet binder..,,something that will pull with control. Bolt a puller bracket to the hinge mount. Attach pulling tool to tree, attach it's chain to bracket and pull pillar or whatever needs pulled....or weld a puller bracket to wherever it needs to pull. Sounds crude but it's all the same as a shop would do without the tree. You are not talking much movement so go slow and stop and try fits.
You MUST use a pulling device that you can control is very small increments.
Option 2: Use wooden 2 x 4 and a big hammer to work the pillar or whatever to move. You can shape the end of 2 x 4 to match what it pushes against so as not to dent it, just move it/straighten it. Short easy blows, enough for slight movement. Should not need to anchor frame/truck for this. You can use wood as a "strong back" and the other 2x4 as a ram with hammer.
Don't do these if not comfortable or doesn't seem right after you start.
I don't like the idea of detaching or cutting anything. If it went one way it will go back.
But to repeat, I can't see which way things need to go and how much. just approximates with a pic or two. Does not seem major and don't see any structural damage... As in: rips, tears or pulled spot welds. I would pull or bump it back.....testing as I go, not looking for show quality door fit or gap. Original gaps were bigish.
Using a straight edge/level is probably NOT the correct way to measure or use as a reference for bending back to shape, USE THE TRUCK DOORS or whatever truck part needs to fit as your gauges.
