8.25 rear in 69 dart change rear wheel back space?

If it's an A-body rear and your putting it in an A-body car it should be the exact same width as the 7-1/4. Sorry, don't know what back spacing 15x7 wheels need. I've got 15x8 on mine and if I remember right their around 3-3/4 to 4" back spacing. My car is also a Cuda so that might even make a difference.