If there is no tag, then the only real way to know is to open it up and look (unless you happen to have
access to the line setting ticket of the Scout it came out of). I'd be very surprised if they're 3.73s - the axle
gearing tended to get higher in the later Scouts, and I think automatics tended to be geared higher as well.
I'd expect something more like 3.07 or 3.31.
If you don't want to open the diffy just jack up the rear of the vehicle and turn the wheels. The number of driveshaft revolutions as compared to a full wheel revolution will also give the answer you seek.