71 Dart Swinger rear tire fitment

I know you said your Dart has a 15x7 rim on it now and you want to to a 15x8and your not sure on the bolt pattern. My 70 Dart has a 15x7 ralley on it with a 255/60-15 on them and they are sbp. So yours might be sbp and with that you might have to special order a 15x8 rim. Just a thought.