The new rear axle has a 4.89 ratio and is used only with offset rear wheels. The rear wheels must be offset 1/2" (minimum) additional or 1" (maximum).
When ordering the axle it should be specified as "H.D. 8 3/4", 4.89 axle, Fleet Engineering Group Release A-801.
Primary use will be for Darts used in sanctioned dragracing. Owners have found that F/S and F/SA Classes offer an excellent competitive opportunity for the Dodge Dart 273 V-8.