8.75 narrowing in a 72 dart

I pondered the same thing for the same year car. Do the mini tub first and center the wheels/tires you plan to use. Then measure and subtract for your disk setup. A flange to flange measurement that worked for someone else may not work on your car and cause the added expense of custom offset wheels.

Go to the Doctor Diff website for your housing ends, disk setup, and new axles. Dr Diff is a good guy to do business with and even answers his own phone.