15" tire size for 67-69 Dart with B.B.P.

What are we talking here? Fronts? Rears? All the way around?

How do you want the car to sit? Stock? Higher in back?

Front and rear tires, either all the same size or a tad larger in the rear so it fills the wheel well a bit.

205-60R15 is the largest I'm willing to go up front and even then I bet it will rub time to time like it does on my Duster.