As said you would have to code it out.
If you are not sure and can not code it out.
If only two dfferent ones pick up both and take the one you do not need back.
But remember the preload has to be put back to specs.
When replacing the seal.
Check preload before starting and make sure it is right when done.
Also at 81K I would be looking at why the pinion seal failed.
Is it lose? Grass wraped around it? Grove worn in yoke? Rear end vent stopper up? Bad bearings.
Pull inspection plate and check bearings and for metal shavings.
With inspection plate off you can get rear end info off of ring gear.
Gear ratio and sometimes ring gear sise.
Get a good repair manual for help on preload.
This link may help.
http://www.differentials.com/install.html