For rear there is no difference aside from the 79+ 3.70 ratio, and early-77 vs 78 coarse vs fine spline pinion.
For front 68?+ =coarse spline birf, drums,
76-78= odd size fine spline birf, disks, small knuckle stud bolt pattern (less availability of aftermarket birfields and histeer arms)
79- 1/90- standard fine spline birf (same as minitruck and SFA 4skinner), large bolt pattern knuckle studs- high availability of aftm arms
76-78 is more than fine for a street/light trail truck. If you have big birfield breakin plans, 79-later or hybrid axle (any 68+ housing will work with any disk knuckles) is best for aftm avail and spare avail.