Over the last 50 years it has developed a bend in the plane of the diagonal between the corners. ie this meant that one corner was about
3" from the wall when the other three corners were touching the wallI thought it would be an easy fix with a cross made of 1x2" material that fit a cross the back of the stretcher. The arms cross at 90 degrees, so the arms are attached to the stretcher about 6" from each end of the stretcher.
This took out a lot of the bend but still left enough so that the one corner is about 1" from the wall when the other three corners are touching the wall.
Is there any other way to get the leverage to take out the rest of this bend.