I haven't checked yet with Cass aka Dr.Diff. It is my understanding that his axles "are" for converting the small bolt pattern 4'' to the 4 1/2'' for the 7 1/4'' rears. Next spring I will be getting a 72 Dart and plan to do that too.Car will remain a Slant 6.I am a long way off tho..
Best is to send him a e-mail.It may be a day or 2 but he never fails to respond.Great Guy to deal with.