Anyone Use 275/60-15 BFG TAs with Cragar Series 61C Cragar SS on Their Duster?

Do you happen to know whst backspace your 15x8's are? I too have an 8.25 rear. However, my car is a dodge dart sport. I currently have 15x7 rally wheels and they are close on the inner side. I really want to go 15x8 ro 15x10. But not sure if they will fit without rubbing.
The wheels I'm using are 61C Cragar with a backspace of 4.25"