It's a Ratio Adapter Box, guaranteed. If a change is needed, the "rivits" will be ground off and different gearing can be installed. You should look closely at the cases, I doubt if they are really rivits, all of these that I have seen are screwed together with either Phillips head or slotted screws.
Either way its a Ratio Adapter Box. Now quit complaining and check how much your speedo is off, fast or slow, take the box and your driveline info to a speedo shop, and see if I'm right.
Just bustin' on ya,
72longbed