whats the correct back spacing?

http://www.centerlinewheels.com/wheels_fitment.php?mw_id=34&sw_id=371&size=i_15 x 9 in the 4 inch bolt pattern.Thats what we had on the 70 dart i built,it had the stock width a body 8.75 with small bolt pattern,and was minitubbed.You may can call centerline and see if they still offer the 15/9 with 7 inch backspacing http://s212.photobucket.com/albums/cc301/tobysoldblue/?action=view&current=70swinger340.jpg