A body 73 and up vs 72 and older front track width questions.

So after doing some more research, it seems if I have a 10" drum spindle the Willwood brakes will offset my factory drum trackwidth to +.20 if I have a 9" drum spindle it will off set my factory track width to -.08 so I learned that not all pre 73 spindles are created equal, I don't know if a 9" spindle car has the exact front track width is a 10" spindle car, or if a 9" drum spindle is longer. I have a set of 10" and can take measurements if somone has a set of 9" we can compare. I believe the 9" were factory on /6 cars