Biggest tire on 1969 dart

Do some measuring of a rim on your car. I have a 71, so different, but I wound up with 5.5 BS on 15x8 for a 275 tire. It centered it perfect on mine, with the springs inboard roughly 1/2.

Its not hard, just do some measuring. Its the BS that is key to making it fit, and not rub the outer fender.