8 1/4 or 8 3/4 A-Body Rear End Assy. 1973 Dart Swinger

If you are going to the 4 1/2", the 8 1/4" axle would be the cheapest and plenty strong for the slant 6. You'll have to get axles for the 8 3/4 if you go that way. Plus the 8 3/4" is much more expensive in the first place.