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.

Good choices if the rims are close to the stock size, should be a good fit.