factory classic chrysler offset is approx +1/4" (+6.35mm). that means the mount face is offset 1/4" towards the outside of the car from the centerline. backspace varies depending on wheel width. for example, an 8" rim (9" overall width) with +1/4" offset will have 4.75" backspace. a 7" rim (8" overall width) will have 4.25" backspace.

keep offset +/-1/4" of that and you should be fine in most instances.