new tire size question

You may have problems getting a 15x10 rim to fit in the wheel wells of a Dart. Darts have a smaller well than Barracuda's, Dusters or Demon/Dart Sports. If you have ever looked at a picture of the Hemi Darts the wheel well was cut out to make clearance where the Barracuda's weren't.

Before buying anything I would get your self one of the checking gauges (Jegs or Summit) that allows you to set the rim wide, backspacing and diameter and start checking to see what you can fit without relocating the springs inboard or having the wheels/tires sticking out past the quarter panel (i.e, the Papa Johns Camaro from the TV commercials).