New guy with new Dart

Welcome aboard!
Is it all original? Without having seen it, or any paper work (build sheet), most cars of that set-up, will most likely have a 904 trans, and either 7-1/4" or 8-1/4" rear end. If it was an ordered car, original owner could have checked it off with a 727 trans and a 8-1/4" rear. Maybe another member here will have more info than this.