I don't know the visible difference, but if you notice an F-350, look at the diff. They have 10.25"'s, and the differential housing will look the same. Yeah, the axle tubes are grat beg uns, and the shafts aren't much smaller than that of a road tractor's. Get the tag# and post it, we'll compare notes.

 

For some basic pictures of the diff cover to help figure out what you have is, take a look at http://www.drivetrainspecialists.com/categories/ford/