Sagging 67 needs your input

My 67 Barracuda is sagging in the rear. I have thought about having the springs rearched, JC Whitney add a leaf (not sure sould use full leaf or 20") or purchasing new springs. This is a road car and do not want a harsh ride. The springs on it now are factory so they have 40 years on them.

All opinions and experience is welcome.

Thank you