Step 1 - determine the outer bearing diameter of your specific HD wheel - might be different side to side.
Step 2 - remember that your XS uses a 20mm rear axle, and the rear bearings on the stock rear wheel are likely different inside and outside diameters to account for an inner flanged spacer that rides on the inside of the sprocket-side bearing between the inner axle sleeve and the bearing.
Step 3 - order a couple bearings that fit the external diameter of the HD wheel, are the same width as the HD bearings (do some research), and have a 20mm inside diameter.
Step 4 - make a steel inner bearing spacer that spans the distance between the inside surfaces of the bearings - this will ensure you don’t overload the bearings when you install the axle and preload it.
Step 5 - figure out your chainline (again, do some research) and brake alignment, which will guide you toward the width of the external axle spacers you need for both sides. You can either cut down your stockers, or find someone to turn you new ones. Steel tubing with .805 ID doesn’t come in very many wall thicknesses, so you may have to get creative.
Once that’s all done, you should be able to press in your new bearings and spacers, then install as you would any other wheel. Good luck in your quest!
