It almost seems like a design error that the flange on the bag is oriented 90 degrees from where it should be. I have another Givi tank bag on my 07 GS and it fits as it should.
Seems strange.
I bought one of these Givi XS320 bags a couple years ago. I used it on my BMW F800GT, and now on my F900 XR. For whatever reason, Givi chose to make it seem like the XS308 tank bag would only fit certain bikes.
IMHO, the solution was not to modify the tanklock ring on the bike, but to modify the bag by drilling new holes and turning the tanklock fitting on the bottom of the bag 90 degrees. I mean, you could do it either way, but if you use another tanklock bag...you'll be off 90 degrees if you modified the ring on the bike. I already had two other Givi tanklock bags, so it made more sense to modify the XS308 and not screw up the mounting for the others.
Now, you can take this one step further. When I had my Honda NT700V, I bought a Cortech 2.0 tank bag. It fastened with magnets, which was great on my Honda...but which didn't work at all with the plastic "tank" of the BMW F800GT. So I took the tanklock fitting off the Givi XS320 bag and fastened it on the bottom of the Cortech bag. It now works great. To firm up the base like the Givi bag has, I bought a cheap plastic clipboard and cut it to the size I needed.
Chris