Rear axle spring perch width

In effect, yes. Check out the pics I quoted and those Barnes4wd towers. On jeeps with boxed frames it is pretty common to french them in to outboard the shocks without running full width axles.

 

That could be done, example being frame plates welded on and then the mount frenched in. That's more than likely what o would do. That way there's beefy welds along the front edge of the mount. The other thing that would do is help distribute the leverage along the frame and not just localize it to that one area.