Make sure it does not get to wide and get too close to the battery tray and battery (depending on which side you have the filler neck on) I went back to a 26 x 19 howe rad, if your battery is in the boot then a 28 x 19 should fit easy. If you do some notching of the lip on the frame rails you will get a 31 x 19 but that is in a 72 dart which is 1 inch wider than a 68 yes? so maybe 30 inch wide max, wheres that tape