'79 3/4 ton front axle?

[Farmall Doctor]

I always thought I had a Dana 60 front axle under my Chev. It has a GM 14 bolt rear, NP203 transfer case, TH400 trans all behind a 4 bolt 350. I posted a picture of it on another forum and was questioned about the claim of 1 ton axles. It's definately not a Dana 44. Dana axles usually have the model number cast into the diff housing, but mine does not. On the backside of the pot it has some numbers cast to one side and GM3 cast on the other. It has 10 bolts on the cover, and anytime I have ordered brakes or minor parts for it I have always told them to go to the heaviest axle in the book, as it seems there were 3 available. Any info would be appreciated, I'd like to get this straightened out. How does this axle compare to the Dana 60? It carried a snowplow and hauled a backhoe full time for 14 years before I got it, and I also haul old tractors on a trailer. The drivetrain is all original with over 500,000KM.
Thanks,
FD