The topcase carrier is a very good add-on to the F650GS. Even if you don't plan to use a topcase, you still have a reasonable luggage carrier when mounting it. I'll try to give you some hints how to mount it on your bike. The photos are ready now, but I decided to leave scans from the installation manual on the page, additionally.
Mounting the set is not too difficult, it should take you not more than 45 minutes.
The complete set contains:
One remark first. Letter indices in the next pictures mark things you'll find on your bike. Figure indices refer to figures in the shipment picture.
Open stowage compartment lid. Remove the two cable ties which secure the tail
light cable (A) to screw fastening points of retaining plate. Position
retaining plate (4) and secure with the two bolts (5). Unlike shown in
manual's graphic, you have to position the retaining plate behind the
fastening points (the picture I took will show this).
Be sure to route the tail light cable in front of retaining plate,
and do not trap it.
Remove the 2 bolts (A) and washers (B). Position bracket (2) and align to longitudinal axis of your bike. Secure bracket with new screws (7) and (6).
Position topcase mount (2) and align to longitudinal axis of your bike. Secure topcase mount to bracket (3) with the four black screws (8) and the two additional washers (9).
Insert key (G) into the lock barrel of the storage compartment lid (D). Attention!
For the next steps never withdraw the key from the removed lock barrel!
Carefully drive out the hallow dowel pin (F). Any tool with a diameter of appr.
2 mm works, f.e. a 2 mm drill.
Unlike described in the installation manual, I didn't find the retaining tab
(H) on my bike. If you should find this on your, proceed with the appropriate
instruction in the manual, else simply remove the catch (E) and withdraw the
lock barrel with key from the storage compartment lid. Insert the
lock barrel into new compartment storage lid (1) until it sits firmly. Position
catch (E) and secure with the hallow dowel pin. If you should happen to find one
in your kit, use this one, else use the old one.
Fit new stowage compartment lid (1) and lock it. Check the width of the two Fit new stowage compartment lid (1) and lock it. Check the width of the two gaps (11). Both gaps should be equally wide and parallel. If gaps are uneven, the topcase carrier has to be realigned (step 3). Misalignment may cause the locking mechanism not to lock properly.
... and ready. Looks quite well, IMHO