I used ghost brackets and modified the harley fat boy bags mounting holesThe picture link you captured used some tubing from the foot peg to one of the grab rail bolt positions. Honda/cobra luggage racks use the front and middle grab rail holes.
Most other luggage racks use the middle and rear bolts. Rear bolt is smaller than the
middle and front bolts.
I jsut wanted to document what i went through to get some brackets made for my 2003 1800C to get these harley davidson hard bags i bought from my neighbor. I wanted them to be secure but still removable if ever i wanted them taken off or for tire changes. which should be fewer now i am on a CT...www.vtxoa.com