I know for the cobra sissybar you don't. The bracket mounts under the fender and wraps around the sides. I don't like how the sabre sissybars mess the lines up. I modified the fury sissybar to fit my sabre. Looks much better IMO. I have a thread on it a few posts down.
Thanks Breybok. I checked out Cobra and they are not as bad as the Honda mounts. At least you don't have to drill holes. They mount under the fender.
Thanks for the info and at least it guided me in the right direction.