The specifics of converting an E Body 8 3/4 rear end housing to an A body 8 3/4 rear end houseing

what wheel specifically? wheel offset plays into it as well. when I measured my duster, the 7.25 rear is 57.125" wide drum face to drum face (where the wheel mounts). the factory SBP rims are 14x5.5 and measure 3.75" BS (so +1/2" offset). when I measured the tires to the inner fenderwell and the inside of the wheelwell lip, the tires are about perfectly centered. if you're using a 0 offset wheel, the rear would need to be an inch narrower to get the tire centered again. if you plan on using a high offset wheel (like a Mustang Bullit, which is +30mm/1.2" offset), you'd want the rear 1.4" wider, which would put you at about 58.5" wide to get the tire centered again....if you wanted to use say, late model mustang rims (2005-newer, +45mm, 1.75" offset), you'd want the rear to be more like 2.5" wider than factory A body spec.....