Then your going to need to measure unless you know for sure the hub to hub is the same as a factory A-body rear. Its easy to do with a square and tape measure if you have a rim off one side, but I suggest you do both sides, as the rear end may not be centered, production tolerances vary and who knows what has gone on with the car in the last 48 years. Or buy the Percy wheel rite. Just remember a rim is about 1" wider than the spec, i.e. an 8" wide rim is measured from the inside of the bead, so the outside dimension will be around 9", you need to consider this if using backspacing for fitment and shopping (this is why using offset is better, it takes the true rim width out of the equation).