Hi Max,
I recently asked the same question on here but it really came down to just trying the LiPo's I had. I recently brought a second hand Cat SX2 and the LiPo's I were using in my Cougar SV fit fine, Losi Xcelorin 6000mah stick packs:
http://www.apexmodels.com/gbu0-prodshow/LOSB9877.html
They do run however extremely close the the pulleys and belt, yet I've run the car for a whole meeting and numerous practices at my local track and they have been fine, and no signs of rubbing on the LiPo atall. Although clear of the main belt and pulleys, I had to tape a small amount of packing to the back of my steering servo to ensure that the LiPo didn't get pushed to far into the chassis, as it would then rub the underside of the front belt which drops down over the belt tensioner behind the servo area.
Hope this helps!
Alex