the A body 8&3/4 would be the narrowest & be a direct fit as far as pads/pinion angle but it'd have SBP axles & I'm assuming your Duster 7&1/4 is BBP & there'd be the extra weight of the 8&3/4 but I'm assuming this is going to be a performance build so yes the 8&3/4 would be needed & that you are also going to purchase BBP axles. I'm sure someone who has a Duster with an 8&3/4 will post what size wheels/tires will fit (iirc they have a large wheelwell flare).