I've had a Givi rack on the back of my ST1100 for some time.
 

With the Givi rack removed,
the Giv rails remain.

Near the rear of each rail are the threaded holes into which the new rack was secured.

I've marked holes to match the Givi's rails on the Sears rack.

Voila!  Holes.

Used the same hex-head bolts from the Givi.

Removing the plugs covering the rail mounting bolts helped the Sears rack fit more snugly/balanced.