Barracuda spring sag in rear.

I added a second long leaf from eye to eye on a 73 Dart I once had. It was a bit cheaper than other solutions.Didnt make much difference in ride height. But it didnt sag much either with hundreds of pounds of tools in there.
If its ride height you need, Im thinking theres only 2 solutions; 1) SS springs, or 2) a re-arch of the current springs.
But those 68 Bcuda wheelhouses are really big. I fit 325/50-15s in mine, at near stock ride height. 295s are easy.