Thanks I’ll try thatyou'll have to determine which side is 'good' and secure that one to an immovable object THEN try the threaded rod trick.
if you don't secure the good side, tightening the rod may bend the good side towards the bad.
when I do this , I tighten a full turn, then pause for 10-15 seconds, repeat until it's parallel, then do it 2 more times, then go have lunch, 1/2 hr later, come back and undo the nuts on rod, measure. It may take 1-2 more turns to get parallel as the steel will 'bounce back' a bit.