Rally Wheel Backspace

Looking to put 15x8 Wheel Vintique rally wheels on the rear of my 73 Duster. The ones I am looking at are 4.5" backspace. Will this work ok with stock height rear, SS springs with a leaf removed on each side, 255/60/15 rear tires? Or do I need another backspace? I will be running 15x7s in the front.