Got some more and better pics of the '79 axle?
From the looks of the pic, its not a '79 but rather a pre-'77 axle. The caliper backing plates are the 1st design which puts it in the pre-'77 category.
Measure the tubes. If they're 2.75" in diameter, its 1st design.
Check the position of the stabilizer mount on the tube. If its by the passenger side spring perch, its 1st design. If in the middle, its 2nd design.
Check the tie rod. If the threads point down, its 1st design. If they point up, 2nd design.
I'm betting the '79 is actually an older axle.