67 Dart Rear tires

hemidart67 said
Going to a 275/35/18 only changes the tire height not width

Right, but with the proper backspacing and trimming you'd be able to fit it in. From what I know a 275/40/18 would be too tall and start hitting the tubs. That's almost a 27" tall and 11" wide vs being a little less than 26" tall.