So just how good was the A-Body back in its day?

I like to point out that back in the day Chrysler never made a "bad" motor.
But people with good memories can name lemon motors that GM made. Maybe some Ford ones too.
"Extra care in engineering" is what they said
The cars you asked about were work horses, grocery getters, working man cars. But dress them up or put a hot small block in them and watch them go. Same torsion bar suspension as the T/A , AAR and Imperial. (Why change it now?)
Very well balanced cars. Considered small cars back in the day. Just the right size now.
Three words: "Flying Green Brick".