Externally, they look the same as the open diff version. You would only really be able to tell if it's a No-Spin by either seeing if both axles turn the same direction when one side is turned, and you can't hold one side still when the other is turned, or by opening it up and pulling the carrier, splitting it, and looking inside.
Here's an exploded veiw of the HO 52/72 differential. The No-Spin components would take the place of the spider gears inside the carrier. The third members interchange from '47-'72.
Here is an exploded veiw of a No-Spin/Detroit Locker.
