E150 Differential Identification

I have a 2002 E150 van. My repair manual, a Haynes production, notes that this van may have two models of differential.
Ford 9.75 inch and Model 60 axles
Ford 8.8 inch and Model 70 axles
What is the inch dimension referring to? How would I determine which differential model I have?
The identifier tag on the differential has the following numbers     3 S 711E     L 55975 2B15
Thanks, William
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