Widest width Tire, Front/Rear on '65 Dart

it all depends on the backspacing of your wheels. I can tell you that, on a 14"x8" wheel with 4" backspace, a 245/60/14 tire will rub on the wheelwell lip.
I'm running a 215/70/14 tire on 14"x6"rims with the same 4" backspace in the front and I had to fold back the lower front corner of the front wheelwell for clearance when turning. Its not visible, though.
Keep in mind that these cars mostly came with tiny 13" wheels.
-Tim