Shortening a rear for the 66 Dart.

Well I,ve come to face reality(rims)and have decided to have a C body housing shortend along with my axels.What width will I need to shorten it to?Also how much needs to be taken off the axels?(moser,s)I want to run 10x15 rims under the 66 Dart.Any help will be appreaciated.Thanks