Width between the Wheel Mounting Surfaces.
Spring perch location.
Shock perches may or may not be in the right place.
Aside from that, there aren't many variables left. The pinion yoke probably won't match the U-joint on your 1/2-ton driveshaft (though my later model axle yoke did).
FWIW, that axle should be a 41/10 gear combination, so 4.10:1, not 4.11:1 ratio.
If you were to buy it, would you be running the old brakes, or converting to something more modern? The old brake drums sit behind the hub, so the entire end of the axle gets disassembled while servicing the brakes. It's a pain, to say the least.