Safe Tire Size bet for 71 Dart Cruiser
205/70-14 is a great tire on a Swinger. 215/70-14 is anothere great size for the Swinger.
I run 215/70-14 on my 65 and 70 Darts. I would stay away from the Super Stock springs, unless you are drag racing. If you need to rebuild the rear suspension, some stock replacement springs would be my choice.