I have added a housing and axle calculator that will help you determine the specs of Mopar 8 3/4″, Dana 60, and Ford 9″ rearends. If you know the housing measurements, it will calculate the axle lengths. Likewise, if you have existing axles and want to build a housing around them, enter the axle dimensions and it will derive the housing measurements.
The calculator assumes DoctorDiff standard “brake gap” by default, although this can be overridden. Mopar-spec brakes will work with the default values, but anything else should be verified. If the brake gap is too narrow for your brakes, they will not fit.
If you are re-using an existing housing, verify that all calculated values match your housing’s measurements! If they don’t, you have entered something wrong or your chosen brake gap will not work!