As Skitter302 advised.
A previous owner/shops may have swapped components since new.
I made a mistake many years ago by telling someone to use the Driver's side label to ID their Rear Differential (axle, pumpkin type, etc.); turned out that a previous owner had swapped a Dana 60 in place of the stock 9 inch,
so, Information, History, ID, pics, etc.:
Differential, 9", 8.8", 10.25" & Dana 44 front pics in 80 through 96 by Kenneth C. @ http://www.badshoeproductions.com/rear.html
Here are the 1989 Ford Bronco EVTM, Emissions (yellowish/red book cover) & Pre-Delivery Manuals, Partial via mrnewland1 in Google Drive @ 1989 Service manual - Google Drive
Slow scrolling, so download for faster viewing and to see the table of contents, the search feature, etc.