what size slick

Asked once before without much an answer. I have a 71 dart with coil overs and a ladder suspension . I wanna know wide of a slick I can run under my car and what back spacing is needed ro run it. Obviously leaf spring interference wont be an issue. I wanna run a short tire because of my 3.23 gear... Thanks

Stock wheelhouse? I'd say easily a 10.5, possibly an 11.5 if you massage the wheel openings.