The Explorer mounts the axle OVER the springs whereas the Ranger mounts the axle UNDER the springs.
The Explorer springs are a nice upgrade for a Ranger or BII and bolt right in after flipping the spring center bolt (if you are going to mount the axle over the springs).
If you bolt an Explorer axle into a Ranger without moving the perches it will lower the rear approx 4 inches, which can be desirable for some street trucks. You will still need to weld on shock mounts though.
For a 4x4, you have to mount new spring perches on top of the axle.
As for the driveshaft, you may need the flange on the end of the driveshaft to make it mate to the Explorer axle.