Widest tire on early b body rear end

My goal is the fit a 295 tire under my 72 Duster with 68-70 Body rear with springs relocated an trim wheel wells an a deep offset wheel(6.5-7 inches)I've been researching as much as I can an seems that I need a 68-70 B body rear but came across a super nice earlier b-body that was in a 70 charger but turned out to measure narrower than 68-70 specs at 54 1/4 ... My question is whats the widest tire you have been able to fit with the 5/8 difference?.... I was trying to get away with spacers but should I be concerned if I have to use a spacer alittle over 1/4 inch ?