One front wheel sit farther forward than the other????????????

My 64 Dart is the same way. When I was fitting for the american racing wheels years ago I had them mount a tire and we mounted it on the drivers side and everything cleared. Well after having the other side mounted and making a turn I found out the same thing you did. Passenger side was farther forward. We ended up modifying the fender. When I was restoring my Dart I tore my car down the the unibody and I never saw any signs of a wreck. Also I measured from front to rear using centerline of rims and could not find 5/8 difference from drivers side to passenger side. I did use disc brakes from a newer a-body. After fixing my car to have clearance I started to look at other a-bodies and most had the same thing going on the passenger side. Jayson