Rear end ID help

This rear end was under my Merc project when I got it and I was told its a 7 3/4 Chrysler. I havnt been able to find anything that says that rear was even produced. There is an 8 3/4 so I thought it might have been a typo, but it doesnt look the same to me. It's about 54" backing plate to backing plate. Thanks for any insight.