You'll have to:
1) Find out what threads those are in the frame. Try using a known bolt.
2) Check the diameter of the stock bolt
3) Hope that adding a helicoil or time-sert will reduce that hole to the diameter you need regardless of threads.
a) If the threads are the same or can be adapted (by using a time-sert) your GTG.
b) If the threads can't be changed (by using a Heli-coil), get a bolt the right thread for the heli-coil and the right diameter for the mount and use a thick fender washer under the head of the bolt. It will be a fine permanent fix.
Don't know about an XB9 but I would think it is the same as on my Ulys - there is a factory thread insert that is meant to go in the frame and the mounting bolt threads into that.
See item 12 in the pic below taken from the parts manual.
For my '06 X that part number is 12 C0028.02A8A - Thread Insert
There is also a screw holding a snubber that is supposed to be in that smaller hole - see parts 7 and 21 below.
7 AN0805.5CSS - Screw
21 L0506.02A8 - SNUBBER, Front Isolator
Engine Mount.jpg
http://buellmods.com/ Maybe helpful to you .