Let's talk about Super Stock springs

My son Aaron (DartThis74) bought some used Super Stock springs for his '74 Duster. We need to replace the bushings, so I got out the tape measure. The front eyes measure 1-1/2" dia. and have 7/16" bolt holes. I checked the bolt size on his '74 Dart Sport and '74 Duster and they both have 9/16" bolts through their front bushings.

First question: What constitutes "Super Stock" springs? Is it merely the spring rate (or stiffness)?

Second question: What does the bolt dia. tell me about the SS springs? Is this just an indication of the age of the springs, or did they all use the smaller bolts?

Third question: What should we look for as far as bushings? Can we get 1-1/2" dia. bushings with the larger bolt holes, so we can use the Duster's existing hardware? Who has them?

Thanks for any input,
Jerry