15 inch steel wheel measurements

Factory mopar 15x7 steel wheels have a 4.25'' backspace. I have used the 4.25'' rule of thumb and have had no problems under early A's B's and the 67up Dart/Valiant that have a smaller wheel house that the Duster/Demon.I have run up to 245/60/15 on a 67 Dart with plenty of room left for the next larger tire.I agree with Steven190 above. 4.25 or 4.5 you should be ok on a 69 A.