Tire fitment
I don`t know squat about dusters, and that body style. But u ,might try 3/4" offset spring hangars, w/ a little massaging a few spots in the inner wheel house, and stretching the front of the rear wheel well opening, (make it the same as the stock shape, and take it clear to the inner body panel) , I did, and have 295 65 15 d.r. on a 68 fastback, w/ no rubbing, on a complete caltrac set up. Not sure, but I always thot the 67-69 barracudas had the smallest wheel openings in the rear, and the smallest engine bays. I know my engine bay sure looks smaller than others w/ r/blocks in them.