Time for new wheels and tires

My71 duster is pretty much the same car as your demon. Rears are 15x8 with a 4.5" backspace and a 275/60/15 fits no rubbing. A 255/60/15 fits well on an 8 " wheel as well, nice sidewall to it. Fronts are 15x6 with a 205/70/15 no rubbing at all.