Doing some maintenance and have some pics for you christian.
Here is the underside of the tank:
Note there are two mounting points, both are recievers that slide onto rubber pucks or spools (for lack of technical terms).
Here is the bike underneath the tank:
The part I am calling a spool is near the centerline of the bike (follow the spark plug wire up and where it disappears is the spool), the part I am calling a puck is distal, attached to the front subframe (the fork is directly behind it)... so you will need the subframe to mount the tank properly.
Other than that, the tank rests on the main frame and is secured by a bolt that comes off of the rear subframe under the seat:
You can see the stud sticking straight on the right.
Hope that helps!