New Poster with Differential ID question

[swiftwater15]

I'm restoring my grandads '72 Fleetside, the truck I learned to drive in. I'm trying to Id the rear axle. It was a ranch truck with 64k original miles, but most of them at about 10 mph bouncing around the dirt roads.

12 bolts holding the rear cover. "GM60" cast into the front driver's side of the casting. "NF3896838" cast into the passenger side casting. Five bolt axles, with 16" rims and heavy spring options.

If this a Dana 60, GM 12 bolt or . . .?

Thanks in advance. Tried a search and didn't find an answer.

Dan