Time for new tires and rims for the 68 Dart
Your problem is the rear axle. depending on the year, a B-body rear axle is 2-6" wider than a standard A-body. You need to know your total width to determine proper backspace for fender clearance. Your picture shows how far out the brake drum is in relation to the fender.
A-body drum to drum '66 to '72 = 57 1/2"
B-body drum to drum '65 to '67 =59 1/2" '68 to '70 = 60 1/2" '71 to '74 = 63"
