Here are some of the steps involved in installing Honda Sabre fenders on a Shadow Spirit:
1. Remove the stock Spirit fenders.
2. Modify the Sabre fenders to fit the Spirit. This may involve cutting, drilling, and/or welding.
3. Fabricate new mounting brackets, or modify the existing Spirit fender brackets, to accommodate the Sabre fenders.
4. Install the Sabre fenders on the Spirit.
5. Make any necessary adjustments to the fenders and mounting brackets to ensure proper fit and alignment.
It is important to note that this modification may require some fabrication and mechanical skills. If you are not comfortable performing this work yourself, you may want to consult with a qualified mechanic or motorcycle customization shop.