Do you own a SB and want to upgrade the brakes? If so there are various things you can consider: change stock rubber hoses to braided type (unless they are already); use aftermarket pads. For more radical improvements and cost, swap the caliper and rotor for aftermarket. However in my experience custom brakes can be less reliable (6-pot calipers and 13" floating rotors on my Glide), which were great when working right, but didn't stay that way long.

Using twin Harley calipers and rotors should certainly be worthwhile, although I would also convert to floating rotors and aftermarket pads. I currently have EBC rotors and pads on both wheels.

 

Easiest and cheapest way to increase braking power is to replace the rotor with a Ness Big Brake kit. Bolts right on using their adapter and paired with a new set of EBC pads you will get a huge bump in stopping ability.