741 with extra numbers below it

So I found an 8 3/4 b body rear end out of a 65 dodge for a pretty good price and in the pic under the 741 numbers there is what looks like a 20. Does anyone know what that means? I have an open 741 and there's nothing under the 741 case numbers but I also have a sure grip 741 with the numbers 28 under the 741 Case numbers which makes me think maybe it's a sure grip but I'm not sure. The guy selling won't pull it apart to look and doesn't know anything about it. Anyone have thoughts on this? Feel free to comment lol