The top of the rack fastens to two tapped holes on either side of the bridge at the top of the seat stays. I've noticed that Cannondale touring bikes use an identical bridge. The hole in the center of the bridge is a brake cable stop. Our Magura equipped bike doesn't use it. The Magura brakes clear the rack easily.

The bottom of the rack goes on the inside of the dropouts. The rack was designed for 135mm mountain bike spacing and our tandem is bit wider at 140mm or 145mm. By putting the rack on the inside of the dropouts I didn't have to bend it. Long steel water bottle screws fasten the rack to the upper set of holes in the dropouts. The threads in the dropout are not very strong. A lock nut on the outside of the dropout keeps the screw from working loose.
Back to our tandem.