I have the Xciting 250, smaller sibling to the xc500. As far as I know the only difference between these two scoots is the engine size and thereby the dry weight, 407 pounds vs 473 pounds, making my 250 lighter by 66 pounds. The frame is exactly the same.
It also appears that my engine is mounted higher than the 500's, as there are two lonely threaded holes in the lower part of the frame just forward the center stand. So the 250's engine is not only lighter but as you can see from the picture mounted quite high in the frame.
What I would like to do is to lower my center of gravity by adding 30# to the frame. I'm considering steel plate mounted just below the engine, 7" x 10 3/8" x 1 1/2" thick, bolted through the aforementioned holes and resting on the tubular section of frame. It sounds simple in theory but I know it adds stress to the frame and if it came loose could have devastating results. Anyone have a better idea, I chose a smaller displacement bike so my learning-to-ride teenagers wouldn't get into trouble by grabbing too much throttle, so won't be trading up.