Turning back the clock

I believe you are correct about the steering box being moved for steering shaft (coupler) clearance.
I had to move the box as far over to the left as I could
to gain room for the larger tube hooker headers while fitting a hemi.
By cutting the box mount off the frame and moving it outboard it gave me an additional 1/2" to 3/4".
The pitman arms sector end becomes the limiting factor as to how far left box can be moved.
It will make contact with the lower control arm at the pivot pin end before box touches the frame rail.
All the factory bracing gets cut away during the process.
Looks like the bolt in brace was their fix to get the steering box mounted solid again.