Drain the rear-end lube, and remove the differential cover. You can do this in one step; place a drain pan under the rear-end housing and remove the cover.
Remove the small bolt that holds the cross pin in place, (the cross pin is visible in the center of the differential carrier) and remove the cross pin.
Remove the "C" clips and axles. With the cross pin removed, you can push the axles in towards the center of the rear end, and remove the "C" clips that hold the axles in place. Once the clips have been removed, pull the axles out of the rear end housing.
Remove the spider gears. The spider gears are the four small gears inside the rear end housing. When you remove the axles, the spider gears pretty much fall out on their own. If there are spacers installed behind the spider gears, save these and reinstall them in the same position when installing the mini spool.
Install the two splined parts of the mini spool (and any spacers) where the two larger spider gears were removed, and reinstall the axles and "C" clips.
Slide the two square blocks provided with the mini spool into the slot between the previously installed splined pieces, then rotate the axles until the holes in the square blocks line up with the hole for the cross pin.
Insert the cross pin, and the cross pin retaining bolt. Put a drop of thread locking compound on the threads of the retaining bolt, and tighten the bolt to 25 foot pounds.
Install the differential cover using a new gasket or a bead of RTV sealant. Be careful not to overtighten the cover bolts; torque to five foot pounds.
Fill the differential with fresh gear lube.